[92GTA]

I currently have an AED HO Series Holley 4150 750cfm w/electric choke, 0.5" wooden spacer, and the AED fuel rail. It's set up as it was out of the box in terms of jets, pump shot nozzles, and power valve. Attached is a copy of my carb card with the current specs.

After adjusting the 4 corner idle screws with a vacuum gauge and doing a considerable amount of driving, I believe:

A) My low-speed jets are too large. It runs really rich by looking at the plugs and the exhaust smell. The plugs are a dark cardboard brown and black around the outside. They should be a light-med cardboard brown and not sooty around the outside, correct? Do I go 2 sizes down at a time and go from there?

B) The low-speed pump shot nozzle is too small. It has a hesitation that can kill the engine when not hot by jumping on the throttle even after removing all lash from the accelerator pump arm. Even when hot, the hesitation is there and bad. Best I can describe it is like the engine totally cutting out for a moment. Do I go 1 nozzle size up and go from there?

C) How do I determine if I have the right power valve for my application? I heard there was quick math I could do by using what my manifold vacuum was at peak after tuning the 4 corner idle screws in drive with the e-brake on?


Now, moving onto the oil catch can. I have the passenger side valve cover going into the RAII air cleaner as stock, a breather cap on the driver side valve cover instead of an oil cap, but the PCV breather at the front of my engine valley pan cover is going straight into the giant vacuum port on the back of the Holley (front port on an Edelbrock or stock).

I'm concerned that this is just sucking oil vapour straight into my intake through the carb base. Under heavy throttle even the breather on my driver side valve cover mists out oil. I think this is also contributing to the outside of my spark plugs being black (but totally dry!). Oil literally drips out of that PCV check valve when I've pulled it.

Is it advised to install a catch can between this valley PCV and the carb? Are lots of people here doing this who have an aftermarket setup?

Thanks!

[74Grandville]

I would get an air/fuel meter so you can tell exactly what’s going on in all conditions.

The power valve will depend on you idle vacuum.

Make sure your throttle blades are setup correctly as well as your fuel bowl levels before making any other changes.


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[92GTA]

Originally Posted by 74Grandville

I would get an air/fuel meter so you can tell exactly what’s going on in all conditions.

The power valve will depend on you idle vacuum.

Make sure your throttle blades are setup correctly as well as your fuel bowl levels before making any other changes.


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I plan on going to a Holley EFI this fall/winter so I'm not sure I want to invest in a stand alone o2.


How do I setup the throttle blades? Yes the float levels are correct.



Thanks!

[Schurkey]

Originally Posted by 92GTA

It runs really rich by looking at the plugs and the exhaust smell.

If the exhaust is stinky, and eye-burning, it's more likely that you've got misfire problems. A somewhat rich mixture will be heavy with CO. CO is colorless and odorless.

A misfiring cylinder will load the exhaust with HC. HC is what burns your eyes.

Originally Posted by 92GTA

Now, moving onto the oil catch can. I have the passenger side valve cover going into the RAII air cleaner as stock, a breather cap on the driver side valve cover instead of an oil cap, but the PCV breather at the front of my engine valley pan cover is going straight into the giant vacuum port on the back of the Holley (front port on an Edelbrock or stock).

I'm concerned that this is just sucking oil vapour straight into my intake through the carb base. Under heavy throttle even the breather on my driver side valve cover mists out oil. I think this is also contributing to the outside of my spark plugs being black (but totally dry!). Oil literally drips out of that PCV check valve when I've pulled it.

Is it advised to install a catch can between this valley PCV and the carb? Are lots of people here doing this who have an aftermarket setup?

Thanks!

Forget all about the "catch can".

Either you have a defective or incorrect PCV valve, some other PCV failure, or the engine has EXCESS BLOWBY.

A proper PCV system has (typically 3/8") manifold vacuum to the PCV vavle, and a single fresh-air inlet in the air cleaner. You have two fresh-air inlets, and there's so much blowby that apparently you're flooding both of them with more blowby than the PCV system can accommodate.

FIRST thing you need to verify is that the PCV is working properly. You may need to experiment with various part numbered PCV valves to find one that works with your displacement, cam (and therefore vacuum) profile, and blowby amount. This really sucks because there's zero information about the flow rates of the various PCV valves.

SECOND thing is to verify that the PCV system has proper oil baffles. You should never have oil mist blowing out of the fresh-air inlets, or showing up at the PCV valve. It would take a LOT of blowby to entrain oil mist if the thing is baffled properly.

THIRD thing is to perform a leakdown test on each cylinder. Maybe you can get evidence of a cylinder(s) that are creating the blowby problem.

Wouldn't surprise me that once you fix the blowby problem, the spark plugs clean-up some.

[92GTA]

Hmm, I've checked for a misfire with an IR temp gun and all exhaust ports are a similar temp and I sure don't hear a misfire. All the plugs look totally identical too. Interesting. Maybe I'll just pay a professional shop to do some advanced tuning on my carb as they would have o2 sensors to stick up the exhaust and might be able to figure it out. I just hate to burn the money for only several months of driving before I go EFI.

So I bought the stock looking chrome valve covers with NO oil baffles to clear my rocker arms, are those the baffles you are talking about? I'm just using whatever PCV valve the local auto parts store show is right for the car. Yeah, that would suck buying and trying a bunch of different ones.

I've done a compression and leak-down test and all cylinders are similar. I do believe the ring gaps are too much on this build tho, I think the previous owner wanted to run nitrous occasionally I think he said. I'm not ready to go through the engine tho so I need to figure something out and the catch can seemed like the best idea short of installing a vacuum pump.

[74Grandville]

Throttle blades should be set with the transfer slot squared. You then set the idle with the secondary’s


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[92GTA]

Originally Posted by 74Grandville

Throttle blades should be set with the transfer slot squared. You then set the idle with the secondary’s


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Got it, thanks!! I'll looks for how to do that online. I was just using the idle adjustment screw on the accelerator cable attachment assembly.

[74Grandville]

Burning eyes at idle could also mean the mixture is to lean.

Today’s fuels make reading plugs impossible if it has ethanol in it.


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[92GTA]

Originally Posted by 74Grandville

Burning eyes at idle could also mean the mixture is to lean.

Today’s fuels make reading plugs impossible if it has ethanol in it.


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Yeah we have E10 here in CA. Too lean huh. Hmm. I'll play with it in that direction and see.

[Schurkey]

Originally Posted by 92GTA

I bought the stock looking chrome valve covers with NO oil baffles.

That's a big mistake, and almost certainly a large part of the oil-misting problem.

[Chris65LeMans]

Originally Posted by Schurkey

That's a big mistake, and almost certainly a large part of the oil-misting problem.

+1. With my Offy valve covers, (non-baffled) my engine would spit oil from the passenger side breather during spirited driving. I ordered tall (to clear my rocker arms) baffled ones, and it doesn’t leak a drop anymore.

[92GTA]

Well, I like the look of the stock valve covers

I guess I'll look at buying baffled ones and running the aluminum spacers and just paint the spacers blue to match the block. Will have to wait until I do my new heads/cam/engine refresh next year tho.

[steve25]

If your throttle plates at idle are open more then .040" then the Carb is adding in transfer slot fuel along with idle fuel .
If this is the case then you need to close down the throttle blades some and increase the amount of needed idle air by changing out the idle air bleeds if they are the screw in type, or drill a small hole in each throttle plate to achieve the same result.
You can't truly nail down what power valve you should until you get the motor to idle solid so you can take the needed idle vacuum reading.
Getting in the correct ball park for the power valve rating is done by taking the vacuum reading at idle and then installing a power valve of 1/2 of the idle vacuum reading you have.

[92GTA]

Originally Posted by steve25

If your throttle plates at idle are open more then .040" then the Carb is adding in transfer slot fuel along with idle fuel .
If this is the case then you need to close down the throttle blades some and increase the amount of needed idle air by changing out the idle air bleeds if they are the screw in type, or drill a small hole in each throttle plate to achieve the same result.
You can't truly nail down what power valve you should until you get the motor to idle solid so you can take the needed idle vacuum reading.
Getting in the correct ball park for the power valve rating is done by taking the vacuum reading at idle and then installing a power valve of 1/2 of the idle vacuum reading you have.

I see, thanks. Fortunately I don't have that idle issue. Looks like I need a 6 powervalve.

[Cliff R]

Unless it's blown out the PV is not a player in the area you are wanting to tune. Jet size may not hit that area either as a butt-ton of fuel at very low throttle openings comes from the idle system and transfer slots on the Holley carb.

The PV is never a player in part throttle tuning at light load because engine vacuum is always well above it's cut-in point. General rule of thumb is to use the highest number PV for early cut-in and best throttle response when you go to heavy or full throttle.

Idle, coasting and light throttle the PV is out of the equation provided the rating on it is below the engines vacuum reading at idle, which it should be for a street engine as most will make 12" or more vacuum at their lowest idle speed.

Modifications to the metering blocks and airbleeds as Steve mentions above will hold the answer to getting the fuel curve cleaned up. Many "high end" Holley and Holley clones will have screw in bleeds, if not they are easily added to a lower end version. For idle fuel most Holley carbs will have plenty, and the exposed transfer slot only becomes a big deal if you have a pretty "hefty" cam and low vacuum and high throttle angle exposing a lot of the slots. At this point it may let in enough idle fuel that you no longer have control at the mixture screws. If you have control and can slow or stall out the engine turning them in then no need to drill throttle plates to add bypass air.

As for crankcase ventilation, the stock system will prove adequate providing you don't have a butt-load of blow by at the rings. I've seen a number of Pontiac engine builds where the stock system was more than adequate for "normal" driving, but when going to full throttle pressure got high enough to blow the dipstick out of the tube, and some oil out the valve cover breather(s). I've even seen a few blow out oil pan gaskets on hard runs!

If the engine is sound and good ring seal a single valve cover breather and factory located PCV in a stock type valley pan is plenty.......Cliff

[Formula jg]

It would be helpful to know some engine specs (cam and intake manifold at least. Also, I hope you take this the right way but it may be wiser to hold off on that EFI until you feel a little more confident with carb tuning basics.

[92GTA]

Originally Posted by Formula jg

It would be helpful to know some engine specs (cam and intake manifold at least. Also, I hope you take this the right way but it may be wiser to hold off on that EFI until you feel a little more confident with carb tuning basics.

COMP Cams XE274H hydraulic flat tappet camshaft, 274/286, .488/.491, 110 LSA

Edelbrock Torker II, professionally ported, integrated nitrous spray bar (250HP shot) from Paul Knippen's Muscle Motors


I didn't want to get into specs because some people here like to make it a pissing contest about what is a good cam or intake combo for the street, etc. I don't give 2 Fs, I have to deal with it and make it run. If you think knowing the specs will help you give me tips on carb tuning principals, then go for it.

I've been tuning FI for 20 years and trust me, it's WAY easier, for me at least. I just broke down and bought and Innovative wideband o2 kit and an IR temp gun for this car to take the guesswork out of it.

[Formula jg]

92 GTA thank you for some of the engine specs.

Can you also provide the following:
float level
IFR size (I don't see it on the carb card pic you posted earlier)
timing details
idle rpm (in N and D) along with vacuum in both those positions

I found out the hard way the key to a great street carb tune is perfecting the basics ie. timing, float level, closed throttle blade position, air fliter housing design, etc.

When you have the right opportunity take the car out for a very low speed test drive. From a stop position start moving by lightly touching the throttle and pay very close attention for any kind of hesitation or stutter. Do not increase throttle angle, keep it steady and the speed should be like you're in a busy parking lot. Repeat a couple of times to get a good sense of what the carb doing.

Next road test, again at the right opportunity, try stacking the throttle. You will need a good stretch of road preferably no traffic. From a stopped position lightly press throttle and hold steady (10mph), then more throttle-hold steady (20mph), continue to 30mph and 40mph. Note what happens ie. smooth transitions, hesitation, jerking, etc.

If you install the O2 prior to these tests it will make the diagnosis much easier but either way just remember the first rule of tunning is to make only 1 change at a time (easier said than done).

[92GTA]

Originally Posted by Formula jg

92 GTA thank you for some of the engine specs.

Can you also provide the following:
float level Perfectly level with the bottom of the clear sight
IFR size (I don't see it on the carb card pic you posted earlier) I have no idea if it's not on the carb card. I'll call AED and ask
timing details 32-36 degress all in (best for my 670 heads on the engine dyno), mechanical advance on my MSD. I *think* 13 degrees at idle, been 2 years since I've checked
idle rpm (in N and D) ~900-950 in N and ~850-900 in D along with vacuum in both those positions Never took measurement of the vacuum in N. It's 10 inches of vacuum in D plus the 4 corner idle screws set 1/16 of a turn rich from peak vacuum.

I found out the hard way the key to a great street carb tune is perfecting the basics ie. timing, float level, closed throttle blade position, air fliter housing design, etc.

When you have the right opportunity take the car out for a very low speed test drive. From a stop position start moving by lightly touching the throttle and pay very close attention for any kind of hesitation or stutter. Do not increase throttle angle, keep it steady and the speed should be like you're in a busy parking lot. Repeat a couple of times to get a good sense of what the carb doing. Smooth as butter

Next road test, again at the right opportunity, try stacking the throttle. You will need a good stretch of road preferably no traffic. From a stopped position lightly press throttle and hold steady (10mph), then more throttle-hold steady (20mph), continue to 30mph and 40mph. Note what happens ie. smooth transitions, hesitation, jerking, etc. Smooth except for the giant hesitation I mentioned in my first post.

If you install the O2 prior to these tests it will make the diagnosis much easier but either way just remember the first rule of tunning is to make only 1 change at a time (easier said than done).

If it helps, all of my cars specs are here: https://www.thefoat.com/92GTA/ride/P...51ED26g%3D%3D/


I'll get the o2 installed this coming weekend hopefully.



Thanks a lot!!!! Alex

[Formula jg]

A lot of goodies in that car, nice ride by the way.

Is the wooden carb spacer open or 4-hole?

What air cleaner housing are you using?

Also ask AED if the IFR’s are located high or low on the metering blocks?

Will you be able to data log with the O2 your installing?