[chiphead]

Aaaand I think I'm in lean-surge land.

I was running .031" IFRs and it was running good but still getting a bit of black soot on the plugs. I reduced the IFRs to .029". Plugs are clean but I'm getting a touch of surge at steady throttle 1700-2100 RPM. That's right when the transition system starts to taper off and the main boosters pick up.

Do I need to go back to .031" IFRs or can I drop the IAB from stock 070 down to 068-066? I'm thinking if I go down on the idle air bleeds, it'll pull a bit more transition fuel and extend the transitions until the mains really start. Am I thinking correctly, and how sensitive are the IABs to size changes?

[Tom Vaught]

Since you are playing with the carb, post up a picture of the metering block with the side showing the emulsion holes in the picture.
Also post the sizes of the emulsion holes on the primary metering block and which ones are not plugged and their position.

Tom V.

[chiphead]

Here you go. It uses a 3-bleed fixed-orifice emulsion package, not the 5 screw-in whiz bang that's all the rage now. For reference, the old-school holleys had a 2 bleed emulsion and the IFR in the low position. This has the screw-in IFRs in the upper position.

The 3 emulsion holes are all .026".
The upper hole near the discharge is also .026". Is that what's called the "kill bleed" for anti-siphon?
The PVCRs are .059
The IFRs are .029
Primary main jet is 70 (stock is 72)
Stock IAB is 70
Stock HSAB is 31

Is there a set of emulsions that I can open to start the main system a bit earlier? Or should I get the wideband system installed first? I'm gathering parts to install my old Innovate LC-1 and XD-16 meter in this car.

[ta man]

I'm assuming you are making idle mixture adjustments with each change?

[Tom Vaught]

Based on the pictures above, try putting a tag wire with a diameter around .020" in the middle of the 3 emulsion holes on each side of the metering block and report back.

The "high" idle feed restriction is not doing you any favors. Lots of carbs run much better with the IFRs in the lower location.
The high position just leans out the calibration too quickly.

Tom V.

[Brentco]

Originally Posted by chiphead

Aaaand I think I'm in lean-surge land.

I was running .031" IFRs and it was running good but still getting a bit of black soot on the plugs. I reduced the IFRs to .029". Plugs are clean but I'm getting a touch of surge at steady throttle 1700-2100 RPM. That's right when the transition system starts to taper off and the main boosters pick up.

Do I need to go back to .031" IFRs or can I drop the IAB from stock 070 down to 068-066? I'm thinking if I go down on the idle air bleeds, it'll pull a bit more transition fuel and extend the transitions until the mains really start. Am I thinking correctly, and how sensitive are the IABs to size changes?

Increasing the size of the IFRs is probably the “better” way to do it. Your reasoning re: the IABs is also correct, however, and is an alternative way to enrich the idle/transition circuit. The air bleeds are less sensitive than the jets, so you might consider starting with a big jump, e.g., around 066 or even a bit smaller. I’ve found results with changing air bleeds can be a bit unpredictable, whereas changes to the IFR show very clear linear changes to the AFR.

Given how much easier it is to access/change the IABs, however, I’d recommend trying that first before opening up the carb to change the IFRs. It’s worth a shot.

Regardless (and in response to your later post), there’s really no point in doing any further testing until you install the wideband. It sounds like you’re quite skilled at divining the fuel calibration based on plugs and lean surges, but compared to the data a wideband will provide you’re still essentially groping around in the dark, IMO. Plugs can tell you whether you’re running rich or lean on average over your total run and over all RPM, but the wideband will pinpoint exactly where and when your AFR is too high or low, and you can adjust the appropriate carb circuits accordingly.

[Tom Vaught]

I have converted many carbs back to the "Lower Position" IFRs.

People always seem to have tuning issues with any carb that has the higher IFR position.

Simplest way is to just install a basic 1850 (600 cfm) or 3310 (780 cfm) metering block
on the primary side of the carb.

But it is your carb. In the time when Holley went to the high mount afr position they
were trying to get the carbs to pass emissions in some states who had idle emissions rules.
You also do not need the 3 emulsion holes on each side of the metering block.

Ask yourself, why did Holley go from a 2 hole per side Emulsion strategy, to a 3 hole, then a 4 hole, then a 5 hole emulsion block"
Because they did not understand how the emulsion circuits worked.

Buy a used Primary Metering Block (at a swap meet), 600 cfm #1850 or 780 cfm #3310, and install it on the Primary Side
if you are afraid to mess with modifying the metering block you have.

The engine will be a lot happier with that simple modification.

Tom V.

[chiphead]

Yup, the carb is worlds better than when I started, thanks to all the great input. The car will cold start cleanly, idle in traffic and performs pretty well overall. It still needs a little help with the transition, but it's very drivable now. The high stall converter really helps a double pumper work on a street engine with steep gears. Otherwise it would be bog city.

I agree that it now needs a wideband. Once you get a carb close , the butt dyno can fool you. It's hard to tell if its rich or lean if it's not surging or smoking or fouling plugs.

What do you guys think of the BLP fully adjustable metering blocks? I like the idea of building a block for it.

[1968GTO421]

Originally Posted by chiphead

Yup, the carb is worlds better than when I started, thanks to all the great input. The car will cold start cleanly, idle in traffic and performs pretty well overall. It still needs a little help with the transition, but it's very drivable now. The high stall converter really helps a double pumper work on a street engine with steep gears. Otherwise it would be bog city.

I agree that it now needs a wideband. Once you get a carb close , the butt dyno can fool you. It's hard to tell if its rich or lean if it's not surging or smoking or fouling plugs.

What do you guys think of the BLP fully adjustable metering blocks? I like the idea of building a block for it.

I checked out their web site and the adjustable metering block looks like a great solution to incorperating Tom's advice in the previous post. I need to look at my old Holley and see if this may solve some issues with it. By the way, great thread, thanks for starting it.

https://blp.com/cart/index.php?main_...ath=65_107_263

[Tom Vaught]

Why Bo Laws builds a great carburetor, as does David Braswell, and for what you are doing you do not need anything other than a stock #3310 primary metering block, but the Bo Laws Part Number: 51251-5R-B metering block would give you the capability to experiment with your calibration when you get the wide band equipment and WOW the strokes at the car shows.

The less than $60 (plus shipping) gives you more things to screw up unless you also have the full assortment of the calibration parts. But it is PRETTY.

Tom V.

[1968GTO421]

Originally Posted by Tom Vaught

I have converted many carbs back to the "Lower Position" IFRs.

People always seem to have tuning issues with any carb that has the higher IFR position.

Simplest way is to just install a basic 1850 (600 cfm) or 3310 (780 cfm) metering block
on the primary side of the carb.

But it is your carb. In the time when Holley went to the high mount afr position they
were trying to get the carbs to pass emissions in some states who had idle emissions rules.
You also do not need the 3 emulsion holes on each side of the metering block.

Ask yourself, why did Holley go from a 2 hole per side Emulsion strategy, to a 3 hole, then a 4 hole, then a 5 hole emulsion block"
Because they did not understand how the emulsion circuits worked.

Buy a used Primary Metering Block (at a swap meet), 600 cfm #1850 or 780 cfm #3310, and install it on the Primary Side
if you are afraid to mess with modifying the metering block you have.

The engine will be a lot happier with that simple modification.

Tom V.

I agree that I would rather use a 3310 metering block but most of the 3310 Holleys my brother and I have found at swap meets had been damaged with problems like stripped theads for the jets and/or power valves. We've found carbs with jets held in with blue locktite. I could just get a new primary metering block from Holley for 3310 carbs:

https://www.holley.com/products/fuel.../parts/134-131

It costs more than the BLP but then chances of a F-U are much less

[Tom Vaught]

I am afraid that with the later casting (obvious in the picture) ribs on the bowl side you would still have the high location IFRs position
and the 3310-5 calibration vs the 3310 -1 or 2 calibration. So for the $100 plus shipping you would still be dealing with a screwed up IFR location.

Tom V.

[Tandyman]

I have used quite a few of these blocks over the last few years . They are a little cheaper.

https://www.holley.com/products/fuel.../parts/134-155

They have the ribs on the bowl side but have the lower IFR's and also have the two traditional emulsions. They typically had .032 IFR's though , and .055 PVR's . The emulsion's have been spotty usually .028 but the last one I got had .031's .
They also come with short 7/8" snap in vent tubes .

Glenn

[Tom Vaught]

Holley # 134-155 is a good metering block to use, I have several on the shelf.
The .032" IFR metering block can be made to work just fine.

The white whistle once shortened slightly can be a much better solution vs the snap in short vents. With the short vents the accel is ok but the "get on the brakes" causes fuel to be dumped into the air horn of the choke tower has been removed. a stall at the wrong time.

Holley originally did most of these design pieces for a reason on the 1850s and 3310s.
What works on a race car may not work well, at all, on a street driven vehicle with good brakes.

Tom V.

[chiphead]

Back at this thing, with the 02 sensor giving me some data.

At idle, the AFR is 12.5-13.0. The idle quality is good, just richer than I'd like. Does not have the eye burning stink. At light cruse, it's lean. AFR flits around 14.5-15.8 with blips to 16-ish at about 1600-2000 RPM. Lean surging for sure. 2000-3000 is 13s AFR on the primaries. I'm breaking in the new 9" rear and haven't hammered on it yet.

I called BLP and they told me to install .082" T-slot restrictions in the main body. This doesn't seem to jiive with the AFRs I'm seeing. They said lowering the IFRs may help, but to try this first. What do you guys think?

[Tom Vaught]

More than one was to "skin a cat".

That high position IFR is screwing things up, though, for you.

I will look at my 3310 stuff and see if I have an extra (used) 3310 metering block.

Tom V.

[jamaca85]

i would change the PV....6.5.....

[chiphead]

OK, here's the latest.

With the stock QF metering block, .029 IFR, .066 IAB, .070 jets, it was rich at curb idle and lean everywhere else at cruise or heavy primaries.

I called BLP and they acted like they didn't want to sell one of their metering blocks. Afraid of comebacks I guess. I got desperate and bought a Proform metering block from Summit.

https://www.summitracing.com/parts/pro-67166c

The one that came in was black and had 4 emulsion holes, not the 3 shown. It does have the timed spark port.

I set it up with
IFR .031 in upper location
Primary IAB .066, Secondary IAB .068
HSAB .031 (stock all 4 corners)
Primary main jet 71, Secondary jets 80
All 4 emulsion holes pinned out at .026"
PVCR .054"

I put it in and let it rip. In short, it ran better than it ever has.

I set the curb idle mix at 13.0-3.5 once it warmed up.
Light 2000 RPM cruise is 14.2-15.5 AFR, but no lean surging, vacuum is 18". Transition to mains is now noticeable.
Once the mains come in above 2000 RPM, the mixture drops from 14.8 to 13.7 on average on flat road.
Any hill climbing, the AFR goes 13.3-12.8 AFR at 2500 RPM. Feels maybe little rich by the butt-o-meter.
Heavy throttle on primaries is good, AFR is flat, goes to 13.0, and stays at 13.0, even below 6.5" of vacuum, when the power valve should have opened.

It's running much better, just by throwing this metering block on the primary. It's headed in the right direction. Where do I go from here?

[Formulajones]

What are you looking for? Those air fuel ratios don't look horrible at all and appear to be in a safe zone.

If it's running better than ever, you appear to have found a happy spot where the engine is working efficiently. I'd be inclined to leave it alone, drive it a while, check MPG, check plugs, and go from there.

Don't get too hung up on AFR numbers, they'll have you chasing your tail. It is an excellent tool though to see how changes in different circuits affect the curve so it has it's usefulness. As long as you're in a safe zone, and you are, and the engine is responding favorably to what you have with good drivability, and it is, I'd say you're pretty close to just fine.

If you want to get picky about WOT power you'll need a chassis dyno or some track time to find the AFR it's happy with there. It might be the 13.0 you have, or it might like to be richer. Only data at the track or dyno will answer that one. Drivability is the key factor, the AFR numbers come second.

[chiphead]

Yup, I'm going to drive it a bit and get a feel for how it runs. It's so much fun to crack the throttle and have the engine actually respond and start pulling. You're right about the temptation to obsess with the settings and not just drive and enjoy the car.

I do like understanding the AFR requirements in detail. Is a cruising AFR in the high 13s too rich? What about high-gear hill climb in the low 13s, high 12s AFRs? Just don't want to waste gas or wash the motor.

If I do need to lean it out 2300-3500 RPM, what emulsion hole do I go after? I assume the "booster gain" is a now bit too high, as it's now pulling fuel very well for a given part throttle opening.