SOME HOLLEY CARB TIPS
 

I am going to try to list a number of solutions to try when working on a Holley Carb.

I will start with the initial engine start or lack of engine start with the carb installed on the engine.

1) Engine will not start:

a) Prime the Carb with fuel
(easiest way to do this is (with a squirt bottle of fuel) by squirting fuel down the vert tubes on the front and rear bowls).

b) Check the Float Level. Using a normal Holley fuel bowl, the fuel should just be BELOW the Hole threads on the fuel bowl with the plug removed.

c) Check the ignition system for spark to the plugs.

2) Backfires thru the Carb

a) Check the Ignition Timing

b) Turn OUT the Mixture Screws

c) RAISE the fuel Level in the Bowls

d) Adjust the Throttle Plates for a "square opening below the throttle blades". Readjust as required.

e) When all else fails, go up two jet sizes on the Primary Main Jets.

3) If the engine has "backfires" thru the Exhaust System

a) Check for Proper Ignition Timing

b) Turn in the Mixture Screws 1/4th of a turn and see if backfires go away.

c) Lower the Float Levels in the Fuel Bowls

d) Adjust the Throttle Plates for a "square opening below the throttle blades". Readjust as required.

e) Lower the size of the Main jets on the Primary side of the carb.

4) If the Fuel Level in the Bowls cannot be set properly.

a) REDUCE the Fuel Pressure to the Carb

b) Remove the Needle & Seat Assemblies and check for grit/foreign material stuck on the needle or seat.

c) Move the Floats thru full travel and check for binding or the Umbrella seal for the Accelerator Pump has not been trimmed to shortest height
(Allows fuel travel of the float).

5) Fuel Shoots out of the Vent Tube on the front or rear bowl.

a) Lower the fuel level in the Fuel Bowl.

b) Remove the Needle & Seat Assemblies and check for grit/foreign material stuck on the needle or seat.

c) Lower the fuel pressure to the carb

d) Move the Floats thru full travel and check for binding or the Umbrella seal for the Accelerator Pump has not been trimmed to shortest height
(Allows fuel travel of the float).

That concludes the initial fire-up checks on the carb. More on the next steps (Engine actually starts and runs) on another post.

Tom V.

Nice, thanks! Waiting on part 2!

Jesus jumpin crimininies... CLIFFFFFF !!! I need a friggen Quadrajet !!!

Just kidding Tom, thanks much, subscribed, "Waiting on part 2".

Edit -:popcorn:


Frank

More Solutions: (The Next Several "Hints" will have a lot of duplication because the same "Items" can cause the Issue with the Holley carb.

6) Idle Mixture Screws 'Do Nothing'

a) Reset the Throttle Plates in the Primary bores
(Adjust the Throttle Plates for a "square opening below the throttle blades". Readjust as required.)

b) Increase the INITIAL IGNITION TIMING

c) Lower the Float Levels

d) Reduce the Fuel Pressure to the Needle and Seat

7) Fuel Leaks from the Throttle Shafts/Carb Base

a) Lower the Float Levels

b) Reduce the Fuel Pressure to the Needle and Seat

c) CLEAN or REPLACE the Needle and Seat Parts (Primary & Secondary)

d) CLEAN THE AIR BLEEDS (Fine wire and carb cleaner for a rinse)

e) Reset the Throttle Plates in the Primary bores
(see above for setting).

8) Fuel Dripping from the carb 'Boosters'

a) Lower the Float Level in the fuel bowl

b) Reduce the Fuel Pressure to the Needle and Seat

c) Reset the Throttle Plates in the Primary bores

9) WILL NOT IDLE DOWN

a) Check Choke 'Fast Idle Cam' to see if holding the throttle blades open.

b) Reset the Throttle Plates in the Primary bores

c) CHECK the INITIAL IGNITION TIMING Distributor may be in wrong position or weights hanging up/too light.

d) Check THROTTLE LINKAGE for improper adjustment of Carb Linkage and Trans Linkage

e) Check 'Dash Pot' (if installed) for sticking

f) Check for VACUUM LEAKS

10) Engine Dies below 1200 RPM

a) Check IDLE SPEED SCREW for setting to high

b) Check Throttle Blade Position

c) Check/Lower the the floats in the bowls

d) Check Ignition Timing

e) Check Idle Mixture Screws for One and a Half
turns out from seated on '2 corner' idle circuit carb

f) Check Idle Mixture Screws for 3/4 turns out from seated on '4 corner' idle circuit carb

11) Engine refuses to stay running

a) CHECK FOR GAS IN FUEL TANK AND GAGE OPERATING PROPERLY

b) Reset Primary Throttle Blades for square window at Transfer slot (Blades may be too low)

c) Open up IDLE EZE screw farther

d) Check Idle Mixture screws (see above)

e) Lower Fuel Levels in Bowls

f) Verify Ignition Timing

12) Spark Plugs show excessive RICH Condition

a) Check Throttle Blade Position

b) Check Mixture Screws for 'too many turns out'

c) Lower fuel Level in fuel bowls

d) Reduce Fuel Pressure

e) Check for idle air Bleeds plugged (run fine wire thru them and then spray with carb cleaner - wear face shield or goggles)

f) Bump up the ifnition Timing a couple of degrees.

(More Tomorrow)

Tom V.

Thanks, Tom, for writing this thread. Despite using Holleys for 40 years, there is always info to learn and re-learn. Appreciate it!

Tom - GREAT THREAD! THANKS!

And while you have directed it toward Holley users, would guess at least 90 percent of your comments are also applicable to other makes.

Jon

Will post more on the Holley Tips tomorrow.
Most of the info will not be on how to tune a Holley or the specific circuits and what they do but on fixing issues with your Pontiac combination.

Tom V.

Good Morning.

I was thinking about Del Forest (A WW-II Mechanics Instructor and My Uncle's Chief Mechanic). Del was a smart guy and a very good instructor.

One of the first things that he taught me was to warm the engine up and VERIFY THE IGNITION TIMING IS CORRECT before messing with the carburetor. He also was big on VISUAL INSPECTIONS of the engine vacuum lines before messing with the Carburetor. He had inspection mirrors so he could look at all of the connections before he removed any of them.

He would find a lot of times that a hose was disconnected, hooked up to the wrong port on the carb, or was bleeding signal from another vacuum device. (Example PCV LINE teed into the Brake Booster Line). This would cause both the Brake system and the Carburetor systems to act strange.

He could build FLAWLESS Rochester Q-Jets that ran perfectly (even on the early carbs).

All that being said. He would many times find an issue where the actual carb on the engine was not the issue. Fuel Pump issues, wrong gas cap on the fuel tank, damaged fuel line going to the fuel pump/engine. He was big on getting the vehicle in the air (Hoist) and visually inspecting the entire fuel delivery system BEFORE messing with the carb. He also typically did a "pre-repair" test drive to see how the vehicle actually drove vs what the customer (or his friendly neighbor) thought the problem was.

He had no issues with adapting to the 70s emissions requirements and plumbing because he was a "Systems" type guy even when teaching in WW-II classrooms.

So my point for today is don't just start pulling off hoses, changing parts, blaming carburetors, before you actually know what the real problem is. Swapping Parts over and over is the last thing you want to do.

Have a great day and a great week-end.

Tom V.

Thanks, the last post there is super advice.

When I first began to learn about Carburetors, Holley Carburetors, from the people who actually designed them in Warren Michigan I was fortunate to see in operation how the carbs were tested for Air Flow and Fuel flow (using Stoddard Solvent). Even though Holley had a 3000+ cfm Air Flow Bench (first built to flow the massive Carburetors used on the Supercharged Aircraft engines built during World War II), Holley preferred to use 8 Flow Benchs that were hooked up to a 8 sliding drums with a precise Constant Volume, Constant Pressure, Constant Temperature design.

The Technician raised the known volume drums by filling them with temperature controlled air until they were fully filled to a precise pressure.

At that point, the carburetor was already installed in a enclosed air chamber and had fuel (stoddards solvent) flowing into the carb fuel bowls. The throttle blades had been set by the Technician for the .020" window in the transfer slot and the choke was fully open.

So then the Technician released the upper drum and for 1 minute it dropped slowly downward and then he read the idle air flow in one minute.

Typically, for most Holley carbs, it was in the 16 to 19 cfm range on the Primary Blades. The Secondary Blades were barely cracked (not touching the walls of the carb base plate). Usually this .020" Throttle Blade setting also matched up with approximately 1-1/2 turns of the Primary Throttle Adjustment Screw.

So the drum was raised several times and the test repeated then the Technician moved on the the next checking point on his test sheet.

After multiple checks, at different Throttle Blade settings, the Technician would have data which could be plotted on an 'airflow vs fuel flow' graph. They did this work for both initial designs for new carbs and for verifying carb production build quality control. Samples of each carb series produced in that month were sent to Warren Michigan for verification of the flow numbers. Holley also had smaller flow stands at the plants for spot checks during production. I observed hundreds of tests but never actually performed a test. That was the Technician's job.

At the end of the day the Carb specs for a given carb model would be checked against a Master Build Carb Sheet with the flow numbers of the Master Carb vs the 'Tested Carb'. Master Carbs were considered to be Perfect Carbs in all circuits of the carb design.

So when you bought a 3310-2 Holley Carb or a 4779-2 Holley Double Pumper Carb, or a 4412-2 Holley 2 BBL you knew exactly what you were getting. In many cases you did not need a whole box of Holley carb jets to dial the thing in for your application because 4 set sizes larger or smaller than what was installed in the carb (stock) typically covered all installations.

All that being said, Holley also had a Test Track to test the carbs on given production vehicles.

They had a Engineering Building with Hundreds of Engineers working in the buildings. They had Engine Dynometers and Chassis Dynomometers as well as two Emissions and F.E. Chassis Dynometers.

Then you had the Calibration Engineers who worked with the OEM people (In those days: Ford, GM and Chrysler) doing constant test drives on vehicles (with the OEM Engineer) using Horiba Air/Fuel Measurement tools costing thousands of dollars (at the time). I still have one of those old test set-ups.

From the web: "HORIBA Automotive Test Systems is a leading supplier in the fields of engine test systems, driveline test systems, brake test systems, wind tunnel balances and emissions test systems. More than just the world's leading supplier of emissions testing systems, HORIBA ATS is able to provide total solutions to its customers, with full turnkey capability."

So everyone who wishes to make their Holley Carburetor better vs the stock piece out of the box (old OEM calibrations) better be on their game.

Have a great weekend!

Tom V.

Today I would like to post some information about the different Holley carburetor systems and how they inter-relate to each other.

A Holley 4 BBL carburetor has two idle circuits (minimum) in each carburetor (one on each side of the primary metering block).
To get fuel (and air for one of those circuits) the following has to happen: Fuel flows from the fuel pump to the Primary Float Bowl thru the Primary Float Bowl Needle and Seat. The Needle and Seat sets the fuel level in the Primary Float Bowl. That fuel level setting is important and should be one of the first things checked if the engine will actually run at idle.

Then the fuel goes thru a Idle Feed Restriction (IFR), with an orifice typically in the .032" to .039" size. This restriction can be enlarged slightly but typically cannot be replaced easily without drilling and installing a new IFR brass bushing. .032" for smaller 585-600 cfm carbs and .038-.039" for 850 cfm carbs.
The IFRs are mounted at the bottom of the main well and idle well channels in most older Holley carb metering blocks.
Fuel goes thru the main jet, into the main well, thru the IFR, and then fills the Idle Well Channel.
When the idle circuit is active, the idle fuel is drawn upward past the idle air bleed and then turns downward as an air and fuel mixture toward the bottom of the Transfer Slot Passage. The Throttle Blade is opened only .020" (if set correctly) so very little idle fuel can pass thru that square opening. Most of the fuel takes a separate route past the Idle Mixture Screw and down the Idle Discharge Passage.
Usually with a 'two idle circuit' carb, the Idle Mixture Screw ends up being about one and 1/2 turns out from being seated.
This idle system seemed to work great for many years.

Some modifiers decided to make the idle fuel distribution more equal at idle and put a Primary Metering Block on the Secondary side of the carb. They duplicated the Idle Discharge Passage on the Primary side of the Carb on the Secondary Side of the carb. This worked well as a modification but Holley was already supplying a small amount if Idle Fuel thru a couple of fixed small holes from the Transfer Slot Circuit to the intake. This original circuit was designed to keep fuel in the secondary bowl from going "Sour" when the driver never used the Secondary barrels of the carb. The tiny hole constantly removed a slight amount of fuel from the secondary fuel bowl and added it to the idle mixture in the intake manifold.
So a 3310-1 carb in reality is a "4 corner idle" carb, except that you can't adjust the idle mixture on the secondary side without drilling out the idle discharge passage holes.

So about 1978, 'young' Holley Engineers decided that they needed to have idle circuits on all 4 corners ADJUSTABLE. So they tried to do the mods like the smart 'Modifiers' and drill the proper circuits. I saw a couple of their carbs with holes drilled right into the main venturi bores of the carb. OOPS! But they figured it out.
So about Carb list number 4779-6 (-6 being the revision number of the carb) the 750 cfm Double Pumper became a 4 Idle Circuit carb (that was ADJUSTABLE. So now the "Turns Out" of the Idle Mixture Screws went from 1-1/2 "Turns Out" to 3/4 "Turns Out" as the idle fuel flow requirement stayed the same but the Idle Mixture instead of being divided by 2 (TWO Idle Mixture Circuits) went to 4 (FOUR Idle Mixture Circuits). Best deal is to TRY to set each idle circuit screw the same number of turns out because if you have one screw at 1.5 turns out then a different screw has to be barely turned out to have the proper idle mixture in the intake.

With a divided (dual plane) intake you can adjust the mixture so that the front right barrel is 1 turn out and the rear barrel is 1/2 turn out but the mixture blends together in the manifold so really you did nothing except play games with the idle screws. THIS IS ON A 4 CIRCUIT IDLE CARB. A normal two circuit idle carb on a dual plane intake has ONE idle screw controlling the mixture for those 4 cylinders and changes in or out of the screw DO make a difference.

With an Open Plenum intake the cylinder that is on the intake stroke grabs air and fuel from anyplace in the plenum it can find it.
Like a clothes washing machine with water dashing in all directions over and over at idle.

So my point is if you have a open plenum intake you really do not need a 4 corner idle circuit carb, a stock 3310 2 corner idle carb will work fine. It will have the low location Idle Feed Restrictions and will supply liquid fuel to the top of the metering block where the idle air bleed will add air in the proper manner. The newer "High Location" Idle Feed Restrictions are another "better idea" that in reality made the idle calibration more difficult to tune. "Shaker455", "Tuner" (from several carb boards), and I always convert carbs back to the low mount idle feed restriction location. And then the carb works like it was designed to work in the old 3310 carb days.

So that is a explanation of the idle circuit, how it works, what a 4 corner idle circuit is, how it works, and why you should have a Idle Feed Restriction and Idle Air Bleed in the locations they are in. By the way a 3310 carb has an Idle Air Bleed in the .070" hole range. a .002" drilling change WILL CHANGE the idle circuit air/fuel ratio.

Tom V.

While I'm privy to the fundamentals, it optimizes my understanding as you bust out the Crayola's, certainly helps richen the picture. :juggle:

I don't stay idle much but when I do, its always nice to come here and get the right mixture of info. :D

I'll stay tuned up, and in, for "the rest of the story". :popcorn:


Again, thanks much!
Frank

A good friend of mine, TUNER, from the Washington State area posts a lot about carbs on the different websites.

He has posted on Speedtalk several times.
A friend of his Mark Whitener (goes by 'jmarkaudio' and Tuner have helped a lot of people on the different boards. Like I help the Boost Guys on this board and as a Moderator on the Turbo Forums board.

So Tuner was having a discussion with some guys on Speedtalk and a lot of misinformation was being posted by people who did not really understand how Holley Carb Circuits work.
I will include a picture from the thread that shows the drillings in the typical carb mainbody and what they do and the circuit they control.

Today's discussion is about the transfer slot, the Transition Circuit, the idle circuit, and a little bit about the main (booster) circuit.

First off, one of the guys in the thread attached
https://speedtalk.com/forum/viewtopi...43705&start=45
thought that the Power Valve Circuit would affect the idle circuit.(Blown Power Valve deal).
As was mentioned in the thread, by Tuner and others, the Power Valve circuit feeds the Main Circuit with extra fuel for Maximum Power needed by the engine. The Main Circuit is used for the vehicle "CRUISE Mode" (Main Jets).

Normally the Primary's Blade Angle of the carbs throttle blades will travel about 22 degrees before the Main System starts flowing. The Throttle blades already have some angle to them so the total travel to WOT is not 90 degrees but about 82 degrees. So 22 degrees is roughly 1/4th of the blade travel (Throttle Opening) before the main circuit starts working completely. Before that point you are in the Transfer Slot circuit which is the discussion for today.

As was said, the Blade angle on the carb should have the Transition Slot covered except for about a .020"-.040" tall window for the slot to be exposed. Most of the fuel is being fed to the idle circuit and its discharge hole in the base of the carb. Between the Idle Feed Restriction and the Idle Air Bleed and the Idle Mixture Screw you can dial the air fuel ratio to a nice 13.5 to 14.5 air fuel ratio at idle. The engine on a street car should idle about 600-700 rpm smoothly and a engine with more power should idle about 1000 rpm (CLEANLY) with a bigger camshaft installed in the engine.

If you remove the Accelerator Pump Lever on the Primary side of the carb and carefully open the throttle blades you can track on your air fuel meter exactly when the main circuit starts to take over from the Transition Circuit. (What the rpm point is, what the air/fuel ratio is, what the air/fuel ratio is when the main circuit starts. These are all little tests that a Holley Carb Engineer does on an actual running engine.
Reinstall the Accelerator Pump lever and you can note what the air/fuel ratio is under a light "Tip-In" of the gas pedal is. Do this a bit and you can tune the Pump Shooters using a air/fuel meter.
Just enough fuel for clean transition between the idle circuit and the main circuit.

So back on the post on Speedtalk.
One of the people there thought that that if the power valve failed it would affect the idle of the engine. As was posted in the thread two completely different circuits. Tuner posted that you could totally remove the main jets (which are much larger vs the Power Valve Channel Restrictions and the engine would still idle fine.
I personally have not done that test as I already know that they are on different circuits.
But read the thread on the Speed Talk link and learn from some real good carb guys like Tuner, jmarkaudio, and others. Mark Whitener is very good with Dominator Carbs. Somewhere is a link to a carb business he runs on the side. Shaker455 also does a nice job on carbs.

So there are literally millions of thread posts out there on how a Holley carb works, some are fact and some are confused mistakes, but on the whole if you look long enough and talk to the right people you can get some good Holley information. That being said, and I posted this before in other threads, at one time Holley bought carbs thru secondary sources in the 70s of about 30 carb modifiers. Of those 30 modifiers, 3 actually made some slight improvements to the carbs for a given application. The other 27 modifiers stuff was for the most part, SMOKE & MIRRORS. That being said, this is not the 70s, we have the internet and some great people passing along accurate info of stuff that works on a carb system.

Have a great day.

Tom V.

The absolute last thing to confirm on ANY Carb before you bolt it on is if the Needle (s) are seating!

Flip the Carb upside down and blow air into it from your Mouth , if you hear air leaking into a fuel bowl then you have a Carb the will flood out on you as soon as the fuel pressure comes up.

Agree, Steve. Do not want fires from flooded Bowls.

Being an old timer, Before I bolt the fuel bowls on, I always check to make sure I cut the installation orange rubber stem off the accelerator pump check valve. It barely let any fuel into the fuel bowl. Everyone makes a mistake due to brain fade occasionally.

Tom V.

Kind of busy today. Ran across a Hot Rod article I had read at one point on Power Tour carb tuning.

Holley had one of their Technical Guys tune several participants engines during the trip.
Basically the tech adjusted the carb for best cruise and f.e. as well as improving HP of the engines.
Using a air/fuel meter, basic tools, and "carb sense".
The Link is here:
http://www.hotrod.com/articles/hrdp-...y-carb-tuning/
A Holley Air/Fuel Meter was used as well as a timing light and carb parts were replaced as required to improve the results.

The reason for this post and the link is to provide some documented actual road numbers for people on a "cruise mode" situation which is the topic for today plus have people identify basic carb/engine screw-ups on the different vehicles. Have fun. There are several owner screw-ups in the article.

Tom V.

Excellent read.
:popcorn:

The owner issues I identified were:
a) Not enough timing on one vehicle for a clean combustion process.
b) Need to replace a metering block after a "carb expert' did his magic.
3) Throttle Blades in the wrong position causing issues with the engine wanting to die below 1000 rpm
4) Selecting the wrong power valve for the application (5.0" power valve changed to 6.5" then back to 5.0" valve after other changes made to the engine system.

There are several more but the point is even with a good air/fuel meter, years of experience, and in this case access to a wheel dynometer, the car still need to drive properly for that specific engine combination.

Lastly. F.E. was optimized for several combinations but some drivers would just like a great running engine and are willing to give up some F.E. for other attributes: (Horsepower, quarter mile times, aggressive driving.)

Have a nice evening and a great Thanksgiving, back after the Holiday on this one.
Next mode is Power Valve, what it does and where.

Tom V.

Just shows many factors come into play, right down to who's behind the wheel and preference. ;)

Like many others I prefer F.E. and H.P., in my youth two tunes a day were required to fill my obsession. :o

In Jacksonville NC there was a huge summer day/night atmospheric fluctuation, the little women and I would cruze the evenings. :cool:

A small adjustment for the cool night air would really make'er twist, car ran a lot better too! :D

Very nice Link, reminds me of going to class an getting to watch a movie :hooray:, have a great Holiday, an Thanks/for/giving.

:popcorn:
Frank

Great info Tom. This thread should be made sticky.

I vote sticky too, and yes, thank you Tom V! I've already sent folks to this thread!

.

Today we will talk about misinformation on Power Valves (specifically Holley Power Valves).

https://www.racingjunk.com/news/2015...ey-carburetor/

I have no clue who Mr Bolig is, really do not care, but he writes guest articles for "racing junk". Apparently he has written a whole series of Guest Column articles for that website. Glad he wants to write articles for people on subjects but the on the carb article on Power Valves he seems a bit confused.

I will try to post the different statements from the article and my comments to the info. You can take my comments for what they are worth to you.

So here we have the article:

QUOTE "When it comes to tuning a Holley carburetor the power valve has always seemed a mystery to many. But, once you know how power-valves work, it’s easy to select, troubleshoot, and install the right one for your application.

1) The power is a vacuum-operated fuel valve that is designed to enrich the fuel flow to the engine under varied vacuum conditions. It is located in the metering block, and opens at a set vacuum that is determined by the spring it contains. Depending on the spring in the power valve, this can occur at varying engine rpm*and directs extra fuel into the carburetor’s main power circuit. The valve itself is a small rubber diaphragm with a small coil spring. When opened, it allows fuel to flow through the calibrated opening in the metering block (power valve channel restrictor). This restrictor determines the amount of additional fuel delivered to the engine.

2) To find out which power valve your high-performance engine needs, you first need to know the vacuum characteristics of your engine.

3) Begin by hooking a vacuum gauge to an intake manifold-vacuum port. Warm up the engine and note the vacuum reading at idle. Automatic transmission equipped vehicles need to be in the Drive position for this test. Once you have a proper reading, divide the vacuum reading number in half. The divided number will determine the correct power valve that you need.

4) Engine vacuum is what actually operates a Holley power valve. The spring that is part of the power valve is the resistance to the diaphragm that only allows it to open at a certain vacuum reading. Spring pressure is what changes the actual operating range of the power valve.

5) As an example, a vacuum reading at idle of 13-inches needs to be divided by two, which results in a number of 6.5. Therefore, you should have a number 65 Holley power valve installed in the carburetor. If your divided number falls on an even number, you should select he next lowest power valve number. For example, a vacuum reading of 8-inches, divided by two and you come up with a number of four. In this case, you would use a 35 power valve.

6) To know which power valve you have, all you need to do is look at it. Each power valve is stamped with a number that indicates the correct vacuum opening point. For example, a power valve with the number 65 stamped on it*will open at 6.5 inches of engine vacuum.

7) Many racers will instinctively remove the power valve and install a plug in its place. This is often done on hardcore race cars that don’t see a lot of street duty. Basically, the power valve is designed to help an engine to deliver a little better gas mileage, and with a race car, fuel mileage is not typically a priority.

8) However, if you decide to remove the power valve, then bigger main jets must be installed. Since the power valve is for fuel enrichment, if it is missing, the engine needs to get the extra, required fuel from somewhere. So, If you decide to do away with the power valve, you must increase the main jet sizes considerably (typically 6 – 10 jet sizes).

9) Knowing what power valve you have is as easy as reading numbers. The face of this power valve has the numbers 6 and 5 on it. That means that this valve opens at 6.5 inches of vacuum.

10) Stock engines typically have a high vacuum reading (10-18 inches at idle) and the Holley power valves with higher readings like 6.5 to 10.5 will work correctly. But, add a long duration non-stock camshaft or other performance related parts, you will soon find out that a stock-rated power valve is not your friend.

11) This is because engine manifold vacuum is usually lowered with these performance parts, and this can cause the power valve to always be open, even at part throttle, leading to an overly rich air/fuel mixture. Holley makes performance style “standard” flow or a high flow power valve, which has a larger opening. If at all possible, avoid any “two-stage” power valve. These are designed more for economy minded users rather than performance enthusiasts.

12) Finally, most of the popular Holley carburetors incorporate a power valve blow-out protection system. This is a special check valve that is located in the base plate, expressly for this purpose. This check valve is designed to be normally open but will quickly close off the internal vacuum passage when a backfire occurs. Once closed, the check valve interrupts the pressure wave caused by the backfire, thus protecting the power valve.

13) If you have a carburetor older than 1992 (or you have experienced an extreme backfire) and expect a blown power valve, use this simple test.*TEST: At idle, turn your idle mixture screws (found on the side of the metering block) all the way in. If your engine dies the power valve is not blown."

14) In a race-only application, some will remove the power valve from the carburetor, and install plugs. If the engine is only ever run at wide-open throttle, this is not a problem, but any street driving*and your fuel economy will take a huge hit. Also, if you plug the power valve hole, you will need to increase your main jets by roughly 6-10 jet sizes." OUOTE

So first off I will let you read the info and then I will discuss the Info and misinformation in this article. I have labeled the 14 statements for easy tracking and discussion.

Tom V.

14) Hate it when people say "remove the Power Valves in a "Race application."
There are so many classes in racing that a generic statement like that usually screws up the guys who Bracket Race and need to leave the line cleanly and have the proper Air/Fuel Ratio throughout the entire run.
You need to determine your specific racing situation and tune all of the circuits for best performance vs "Block both of the Power Valves" as a generic statement.
The Power Valves are only 'the switch'(s) in the carburetor.
The Power Valve Channel Restrictions control the actual fuel flow when the Power Valves are open.
The Power Valve Channel restrictions work from the time that the Power Valve first opens until there is sufficient vacuum in the engine to close the Power Valves.
Also a higher number Power Valve 'leads the Duck" before the Duck and the "Shot" from the shotgun actually get together.
You will always "miss the Duck" if you calibrate for the exact spot where you "see the duck".

The gentleman recommended a idle vacuum number divided by 2 and if on an 'even number' GO LOWER on the Power Valve number.
This way you will be even farther "behind the duck" when you need to be "in front of the Duck".
Holley Engineers used to say: Highest Vacuum Number (because the vacuum dances around with a bumpy camshaft and then divide by 2 and ADD .5 to the number. So 12" of vacuum /2 = 6 PLUS .5 so the correct valve would be a 6.5" valve not a 5.5" Power Valve.
That whole number difference is the difference in smooth performance that discourages racers so they take the valves out completely trying to fix the LEAN MISS.

So we have covered the actual Power Valve switching.

Now the Power Valve Channel Restrictions are controlling added fuel BEFORE the Main Jets really come on line.
It takes more signal to move a big glob of fuel thru a Main Jet quickly vs a smaller amount of fuel thru the Main Jet opening and then on to the Primary Metering Block Power Valve Channel Restrictions.
It should go Idle Circuit, Transition Circuit, Power Valve Channel Restrictions for moderate load, then Main Jets and Power Valve Channel Restrictions Together for WOT. The Booster is working once the main circuit comes on line but the amount of fuel thru the booster is best controlled by Both Circuits working together.

More on this in another post later

Tom V.

Now featured at the top of the Tech Thread Archive thread here in the Pontiac Street forum.

Thank You very much b-man.

Tom V.

So now we talk about #12 & #13

12 & 13) "If you have a carburetor older than 1992 (or you have experienced an extreme backfire) and expect a blown power valve, use this simple test.*TEST: At idle, turn your idle mixture screws (found on the side of the metering block) all the way in. If your engine dies the power valve is not blown."

As was mentioned in a earlier post, you can take the jets completely out of the metering block and the idle will not change because the Main Jet Orifice is much larger in area vs the Idle Feed Restriction which supplies fuel to the Idle Circuit.

So turning in the idle mixture screws all of the way does nothing to prove whether the Power Valve is damaged (Blown) or not.
Another Old Wife's tale that will live forever.

Holley added the tiny spring and ball to the base plate, as the story was going around that if you have a Holley carb, and the Power Valve blows, the Power Valve will allow the engine to syphon fuel from the carb bowl and the fuel will then hydra-lock the engine and damage parts.

Holley Engineers knew that this was Bull**** BUT in order to sell carbs they put in a "anti-backfire" check valve system in the carburetor throttle baseplate.

I have run Holley carbs for over 50 years and have NEVER HAD a single occurrence of a Blown Power Valve.

So a second line item in the article is suspect.

Tom V.

Item 7) Many racers will instinctively remove the power valve and install a plug in its place. This is often done on hardcore race cars that don’t see a lot of street duty. Basically, the power valve is designed to help an engine to deliver a little better gas mileage, and with a race car, fuel mileage is not typically a priority."

Last one tonight

What is instinctively? Most car guys do something because someone else gave them some information, be it good info or bad info.
If a Racer says to another racer, "you are not a 'Real Racer' unless your carb has Power Valve Blocks, 'because my race car has "Power Valve blocks". Same deal for a "Hard Core" Racer vs a Normal Racer. I guess you are hard core if you do a lot of stupid chit without knowing what you are really doing. Engine idles at 1200/1300 rpm, rich as can be, have to rev it up over and over to clean that 'bad boy' out.
That is what a race car engine is supposed to be like according to some.

A Power Valve in reality is just another fine tuning device on a carburetor to make each mode of operation closer to the ideal air/fuel vs power curve.

So screw the air/fuel meter and the different circuits on a well designed carburetor (be it from Holley, or Rochester, or Carter originally).
Make that sucker a On-off switch where the only way it will run is at 6000-7000 rpm minimum and most of the time it waters your eyes to be near the car. Because that is what a "hard core" race car engine is supposed to run like.

People actually read this crap.

Tom V.

ps, Many times at the race track the Holley Tech guy put the carb back close to a stock calibration and told the guy, Go make a pass
and if it runs good, leave it alone.

Tom I agree with you 100%! When I was running my super gas , I got talked into removing the power valves. It will make your car run so much better! It did nothing for on track performance! But driving around the pits and the return road, was a different story. It had a huge flat spot ! I hated the way it drove. I ran it two weekends like that before I put the power valves back in.

Good Morning, So previously I gave you an example of a writer of Holley information who needed a little work with the facts on what he was writing.

So now I will provide a link to a website with only a couple of HOLLEY CARBURETOR TIPS but the tips are well written and give very good information on the subject that they are covering. I have no affiliation with these people, have never met the people, just ran across the info one day doing a search.
So here is the link:

http://www.vintagemusclecarparts.com...s/techsection/

In the Tech Section they have three tabs for Holley Information:
HOLLEY TUNING
FUEL FILTER SERVICE (Covers the internal fuel filter inside a OEM style Holley Fuel Bowl)
Needle and Seat Inspection, Adjustment, etc.

Way too many good pictures (and all are copyrighted) so you will just have to go to the website and read the info and look at the very good pictures on how to do the PROPER ADJUSTMENTS ON THE HOLLEY CARB.

Some nice work here.

Tom V.

Appreciate the ammo, let the feathers fly ! :Peace:

Your knowledge and explanation of the system allows me comprehension, and unlike the Duck, is bulletproof. :)

I understand there should be a courtship between the PVCR and Main Jets via a correct Power Valve. :heh:

I am not a technical guy, like that need be said, an for me a analogy works best at times so here is mine. :D

Allow me to take for example the Jet as a attractive female, and myself being the Fuel. :rolleyes:

In my best James Dean, I hang around doing nothing for the exception of a pose. :cool: (Idle Circuit Mode)

I nonchalantly swagger toward her with the illusion of no interest, ;) (Transition Circuit).

Check my smooth in the mirror, :cool2: (vacuum opening point) proceed to swagger.

(PVCR Moderate Load) check my pecks an throw a "Hey Baby" :nerd:(WOT)!

Correctly done and sequence completed, an acceptable result should be attainable. :oogle:


Looks like another movie day, Much Thanks Tom! :popcorn:
Frank

PS: Never considered myself a Hollier Than Thou guy, or a James Dean type, good thing!

Everything Tom shared in this thread plus selected downloads from the links he provided are going into a binder which will reside on my carburetor reference shelves.

Thanks Tom

Thanks Tom..your advice has helped me over the years.

Thanks very much, I will continue the thread tomorrow.

Tom V.

My sincere apologies for the excessive horse play, my intentions are not to detract from this most valuable, desirable, informative and I might add very appreciable thread.

Some post threads with a question and the illusion they have a answer, you post with the answer!

Looking forward, as you resume, and again much thanks Tom.


:popcorn:
Frank

Please, by all means, do that.

I cannot seem to get enough readable material to look at.

Good, specific, accurate and precise material.

Thanks Tom for spending the time poking on that keyboard!!

Good Evening, Hope everyone had a Great Thanksgiving Holiday.

Tonight I want to talk a little bit about the Holley Accelerator Pump and how to set it Tom's way vs the video (from Holley) that I have attached here: https://www.youtube.com/watch?v=k-Nx5HEzvlY

Watch the Holley Video first then we can discuss my way vs the guy who was doing the video for Holley.

Just a couple of comments first.

I see NO benefit to rapping the accelerator many times to determine if the the accelerator pump is working properly. Just wasting gas after you determine that the pump is delivering the pump shoot to the shooter. Looks cool on the video but gives people the idea that it is necessary and it is not.

But look at the video and then I will discuss this subject further tomorrow.

Tom V.

I can't watch it, "An error occurred. Please try again later." :(

Edit: Ok perhaps I need a You Tube account, got my son here, worked on his phone.


Thanks,
Frank

Just clicked on the link here and it worked fine for me.

Tom V.

Clicked the link this morning.
Video comes up with "MR CARB TUNES GARAGE"
Sorry that it is not working for you.

Overall the info is pretty good. The CONSTANT "working the throttle lever' drives me crazy though in the video.

The assumption when you buy the "Pump Shooter Kit" is that you will be 'totally in the dark' on what your pump shooter size should be. If you bought the right carb for the application the Pump Shooter size should be close to stock.
Now if you are building a bunch of carbs for different people then you will probably use a few more Pump Shooter sizes. Holley wants to sell Carb Jet kits and Pump Shooter kits.

Another assumption is that the Accelerator Pump Linkage (clearance) was set wrong by the factory or the individual before you who owned the carb.

So here is My thoughts on the subject:

1) Remove the carb and make sure that the Throttle Blades are in the correct spot on the Primary side of the carb (Transfer Slot Position)
Make sure that the carb float settings are correct. Do those things first.
Set the engine idle at the proper rpm for your application using the secondary throttle blade position or by drilling holes in the carb blades.
(Drilled Holes in the blades may not be necessary unless the engine is a large engine.)

Make sure the engine is warmed up to operating temperature and the Choke Blade is open fully.
So once you have the carb idling correctly, don't touch the Throttle Speed Screw on the Primary side of the carb.
The assumption is that the Mixture Screws are adjusted properly and now you are ready for some other testing.

In the video, they show adjusting the Accelerator Pump clearances. You can easily do that step on the bench when you are checking out the other systems on the carb.

Remove any air gap between the Accelerator Pump Cam and the Accelerator Pump Lever when the blades are in the Idle Position on the Primary side. You turn the spring retainer and lengthen the distance until the clearance is barely removed. Then you open the throttles completely and you should still be able to push the pump diaphragm a bit more and see clearance on the Accelerator Pump lever.
What you are doing here is making sure that the Accelerator Pump Diaphragm always have some extra movement room. Otherwise you bend carb parts. Liquids for the most part are incompressible.

The "Pump Shooter Sizing" Check is best done on the road, not by blipping the throttle 100 times.
You are checking for instant response on "light Tip-Ins" of the throttle on the Primary side for mostly street applications.

Then you can do a few Short Wide Open Throttle tests and see if the engine accelerates smoothly in that mode without a hesitation. You are checking Acceleration Pump Function here.

In both cases, you should always have a bit of Accelerator Pump Diaphragm Clearance when the Carb is at WOT on the Throttle Blades.

I will discuss Pump Shooters Tomorrow.

Tom V.

"Overall the info is pretty good. The CONSTANT "working the throttle lever' drives me crazy though in the video."

X2..

Tom can I add something? Often I see guys adjusting their idle using the primary blades and not readjusting the pump arm clearance. Any change on front blade position will affect the pump arm clearance..even a small change.

They just have not learned yet that placement of the Primary blades to the transfer slot is one of the major setting on the whole carb.
Idle EZE is a great thing, adjusted secondary blades (for additional idle airflow are second best, holes in the blades are the final option.

Tom V.

One of the posts I will make at some point will be how to mod your carb for 'home built" Idle Eze.
Tom V.

Cool!

A little Bit on "Pump Shooters" (since they were shown in the video - a Tech was changing one on the engine).

I like to remove the Pump Shooter parts off the car engine. (Takes no more that 10 minutes to remove the Holley carb completely from the engine.) I do this because it makes carb changes so much easier (on my back muscles) and fewer scratches on the fenders by helpers.

A Holley Shooter Assy has 4 basic parts:
The "Shooter", the Retaining "Shooter" Bolt, the gasket under the Retaining "Shooter" Bolt, and finally the gasket under the "Shooter" itself.

Now when you build the carb, you can glue the gasket under the "Shooter" to the Holley main body so it does not fall down on the Primary throttle blades when you are trying to install it or you can glue gaskets onto a bunch of Holley Shooters and then do the shooter swap like the Tech did in the video. I have a lot of Holley carbs and order parts for them but they only give you 4 shooter gaskets in a typical kit".
Two gaskets for under the shooter and two gaskets for the shooter retention screws (Double Pumper carb).
So I glue two of them on the carb main body when I have the choke shaft and blade out.

Shooters come in different sizes. .026", .028", .030", .031" etc. You can buy Shooter Kits that give you a whole bunch of them. When I worked for Holley I just bought a Cup Full of Shooters right from Holley of the smallest drilled size and then drilled them out for each application. If I drill one out and it is too much shooter volume too quickly then I put a smaller one in and put the modded shooter in the "square" in the box for the new drilled size. 40 Years later I still have a few small hole shooters left and have done a few carbs (lol) in that 40 years.
My shooters were the basic ones. Not "Shrouded" and not the "Extended Nozzle" type. The "Shrouded" nozzles were used on a lot of the 650 and 800 cfm Spread Bore Carbs. The "Extended Nozzle" were for specific applications but can't give you what they were off the top of my head.
Mostly aftermarket carbs.

The "Shrouded" Nozzle shooters were called "Anti-Pull over" shooters if you want to be correct on the name. Sometimes the air velocity past the shooter was strong enough that the shooter would see a slight vacuum and would pull some of the fuel out of the shooter. Not enough to pull fuel and raise the shooter 'check needle' but pull fuel from above the check needle.
The check needle is raised up off its seat by the pump diaphragm pushing fuel past it when the pump is depressed. I always take an old steel check needle and lightly make a proper seat around the Shooter nozzle hole inside the main body. Drop the old needle in the hole, insert a thin drift punch, set the punch on the steel needle, give it a light tap, and then turn over the carb and let the old steel check needle fall on a carb tray for use the next time. Now the gas above the check needle can't leak back to the fuel bowl.
If you have a metering block with a metered orifice on that circuit on the fuel metering block, it is there for a reason.
They put that orifice on some carbs as a anti-heat (fuel expansion) bleed if the pump diaphragm/housing is in a hot engine compartment next to a hot manifold.

The Extended Nozzle shooters have the capability to blast fuel from the shooter and have it actually hit the carb booster. When that happens the fuel is immediately mixed with the air rushing past the carb booster in the venturi area. Works well with larger carbs that want the pump shot fuel mixed immediately before entering the intake.

So again, you do not need to rap the throttle 50 times to verify the shooter is working.

You do need to check the accelerator pump adjustment every time you change the idle blade position on the carb (as mentioned by ta man).
Primary or Secondary positions.

I will discuss Accelerator Pump Volume and vehicle applications (swapping 50cc pump and 30cc pump on the carb) tomorrow but will mention that when the pump moves, and the fuel shoots from the shooter, a 30 cc pump is based on 10 shooter strokes of the pump in a collection vial. So each "stroke" of a 30cc pump is 3 cc and each stroke of a 50cc pump is 5 cc of gasoline. Mr "Rap the throttle 50 times" just put 75cc or more of fuel thru the engine that was not needed and just wasted it for the Video Show.

Tom V.

Here is a nice PDF file (No Video just easy to read words from Holley). It was printed in 2007 and was updated in 2014.

I mentioned above about Accelerator Pump Shooters and mentioned a few sizes. "Shooters come in different sizes. .026", .028", .030", .031" etc."
The PDF says that Pump Nozzle Sizes are available from .025" to .052". I was not aware of the .052" pump shooter.
"Please note that whenever a .040" or larger accelerator pump nozzle is installed the “hollow” pump screw should also be used."
I personally put in the Hollow Screw at around a .035" shooter or if I am using a 50cc pump on the Primary side of the carb.
Cliff Ruggles and others saw an improvement in their carb tuning efforts by adding that system.
50cc pump and hardware on Primary side of carb, 30cc pump and hardware on secondary side of pump.

I have actually had a person stand close to me when working on a carb and the person say "Hey Dude, you installed the carb backwards."
The Mod works well with Auto Trans cars and a tighter converters.

The Holley PDF say: When changing the pump nozzle it’s best to jump three sizes. For example, if there is currently an off - line hesitation with 28 (.028”) pump nozzle, try a #31 (.031") pump nozzle. Some of the "Rules of Thumb" work pretty well at times. Cam tuning for the Pumps help too.

Holley sells a little Pump Cam Assortment Kit
https://www.holley.com/products/fuel...ts/parts/20-12

9 parts, but the reason why I mention this link is because the Pump Cams are identified: Lightest to Heaviest (pump shot) (Light means a small pump shot into the carb)

"Accelerator pump shot relative to cam color from lightest to heaviest are as follows: Black, Pink, White, Red, Green, Orange, Blue, Brown, Yellow" You do not typically see that info in most magazine articles but it is there if you read a lot of the Holley Info on the web.
The Pink Cam seems to work well in most applications and as you can see you have a lot more choices AFTER that cam.
(That is a Kit worth buying and keeping in your Holley Tuning Parts kit.)

So we have touched on Accelerator Pump adjustment, Cams for the pumps, Shooter Sizes and types, Hollow Screws, and a few other things.
I have a couple more before we stop today.

We have a Accelerator Pump Check Diaphragm installed in the fuel bowl floor of the carb on newer carbs. It is typically orange.
There are also older Holley carbs that had a ball trapped in a retainer that sealed when the pump was activated, otherwise it was open and let fuel into the pump cavity. The Orange Accelerator Pump Check Diaphragm is a better deal.

Remove the old diaphragm, stick the long rubber tip thru the center hole, pull it thru the hole until the retainer "bump" traps it in place and then carefully cut the excess material off the part so that the cut is close to the "retainer bump".
If you do not do this the float will have very little travel and the bowl will have little fuel in it and a hesitation will occur. CUT THE STEM OFF.

Tom V.

Today will talk a bit about the "Idle-Eze Idle Air Control parts. Idle Air By-pass was used for years and years on the Carter AFB Pontiac carbs so Barry Grant did not invent that capability. Other people, like myself, made our own "Air By-pass" systems, (Tri-Power is extremely easy as you can add extra idle air with the end carb throttle blades). But we are talking about the Idle-Eze system that Holley now uses because they own Barry Grant's old Demon company.

This article by Maxchevy.com has great pictures so I will use it for explanation purposes.

http://www.maxchevy.com/printable.ht...20Rough%20Idle

The last paragraph in the article: 'On racing engines, the Race Demon carburetor introduces air at idle via a jet instead of the Idle-Eze.
The jet is supplied either in an un-drilled form or pre-drilled." I have been making 'jets' that fit the center area of Holley Base Plates for years.
You drill thru the air cleaner stud hole down to the cavity inside the main body and now extra air will be on one side of the "control jet" that is installed in the Holley Base Plate. If you do a Blow-thru Carb air cleaner stud mod (hollow stud) then the air comes from that location.
Or you can drill holes in the main body casting and use a solid stud to hold the air cleaner on. This is what Holley does today.
Read the article and it can give you lots of ideas.

Tom V.

"Anti-Pull over shooters"

Do these shooters interchange with standard and long nozzle shooters?

Yep, direct interchange.
Tom V.

Back on the Idle-eze type modification.
I found a old picture in my files of a Old School Holley modded for Idle Air By-pass with the air cleaner stud used to close off part of the air by-pass system to the lower center part of the carb.

Basically the way it works you drill a bypass hole at an angle towards the air cleaner stud boss.
Then you drill a deeper hole downward from the air cleaner stud boss into the cavity in the center of the Holley carb.
Now if you need additional air you back off (raise) the long air cleaner stud (threaded rod) slightly and let more air pass thru the drilled by-pass hole into the center chamber and then on to the area under the 4 throttle blades. Simple, works well and most do not even know it is there. Reinstall the air cleaner and see if the idle has changed slightly with the air cleaner installed.

Some old Chebby carbs had a PCV valve connection on the SIDE if the carb (see Pic) You could take that fitting out and put in a fixed jet that would allow additional air same as the air cleaner stud mod but again hard to find one of those old chebby 3310 type carbs.

Tom V.

Today, I am going to talk a bit about "Holley Carburetor Information". When I worked for Holley we had a book called the "Illustrated Parts & Specs Manual".
Holley Carburetion No 36-51 (Rev 2)
Retain 36-51 (Rev 1) for some discontinued models. 1975

Contents:
Numerical Parts List
Adjustments and Specifications
Service Parts List
T.V. (Typical View) and Carburetor Illustrations.
The Price was 43.00 to have it printed and Holley/ Colt Industries Carburetor Division PO Box 749, Warren, Michigan 48090 was the publisher. The manual was red/orange in color and everyone called it "The Red Book"

It had info on things like
"How to do a 'Dry Float Setting' (Fuel Bowl Inverted)
Automatic Choke Settings
Air Vent Valve Clearance (pre-emissions setting)
Choke Qualifying Dimensions
Float Drop settings
Accelerator Pump Adjustments (even in 1975, Holley said go to WOT, push the diaphragm lever down, and measure the clearance. (To make sure the pump diaphragm was never torn and a gas leak could happen.)
Fuel Pressure settings to the carburetor (and a lot more info).

Holley also came out with Service Guides and one of my bosses (Mike Urich) wrote several Books called HOLLEY CARBURETORS over the years. Can still find those in print.

So then you get into a secton of the book called:
"Variable Specifications and Parts"

The List Numbers start at 388-6AS carb (which was a White 3000 Series 150A Engine Carburetor).
The last List Number in this 1975 book is a List # R-7514-A Carburetor (for a 1975 Mustang 2.3L Engine Auto Trans).

That being said on page 121 of the book we have the FIRST HOLLEY DOUBLE PUMPER CARB LISTED: R-4776AAA A/M 600 CFM W/Dual Diaph Pump It gives the Illustration Page for the carburetor 34-1 It also gives the part numbers for the different carb parts. 34-1 Illustration starts on page 241 and goes to page 243 (with two illustrations
The first Part on the list is the Choke Plate and 205 parts later is the Choke Thermostat lever.

I bring this up because each carb series part (4150) kept that illustration number. So Illustration Part # 101 is "Main Metering Body and Plugs Assy - Primary" and Part # 102 is "Main Metering Body and Plugs Assy - Secondary".

So now we know that the Metering Block Numbers for a 4150 style carb will always be basic Part Number "101 & 102".

So all that being written, FIRST HOLLEY DOUBLE PUMPER CARB LISTED: R-4776AAA A/M 600 CFM W/Dual Diaph Pump will have stamped on the Primary Metering Block #4776 and 5882A and the Secondary Metering Block #4776 and 6502A on the top (right side) of the metering block. So with the book I can identify any Holley Double Pumper carb (even if the choke tower is milled off and the guy is claiming it is a 800 cfm carb (not a 600 cfm carb) by reading the metering block numbers. The Carb Throttle Plate assy will be stamped with 4790A somewhere on the base.

So that is how the basic Holley Parts Identification system works.

Tom V.

ps I have the 1975 Book, the 1982 Book, and the 1989 Book which pretty much covers all of the Good Holley Performance carb part numbers before the HP series carbs. (The 1989 Book has all of the older Dominator Carb Numbers in it).

SO IT REALLY HELPS BE A HOLLEY CARB "EXPERT" WHEN YOU HAVE THE CORRECT INFO IN A DISCUSSION
(and actually worked for the people and know where to get the actual specs).