[92GTA]

Originally Posted by Formula jg

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

Is the wooden carb spacer open or 4-hole? Open

What air cleaner housing are you using? Factory RAII lower and upper pans with seals, K&N 3x14 round + K&N filter lid

Also ask AED if the IFR’s are located high or low on the metering blocks? Will do, I'll call them tomorrow

Will you be able to data log with the O2 your installing? No, it's just a sensor and a digital gauge. I'm going to strap it to the steering column so I can see it and the tach in real time. With no TPS sensor it's all best guess anyway

Answers above. Thanks!

[Formula jg]

For starters do you have another lid to use in lieu of the K&N? I'm not the only one that had tuning and driving issues related to those type of lids. Replacing it may not resolve your issues but will help eliminate it from the equation.

Have you tried a 4-hole tapered spacer? If no, you may want to consider it, your combo may really like the increased air velocity it provides.

Not being able to data log makes the tuning a little more challenging because it picks up the changes you just don't notice while driving (no matter how much attention and focus you put on that gauge) and it's those split second peaks and valleys in the log that typically need tuning attention. However even without the log capabilities it's still a very useful tool to point us in the right direction.

[92GTA]

I have the stock metal air cleaner lid.

I have not tried a 4 hole spacer, not willing to invest in one either. I really didn't want to get the o2 sensor.

Let me re-frame this a bit and take a step back.... I've already made a purchasing decision to go with an EFI setup in the coming months. I've been driving with this setup as-is for 2.5 years (20K miles) and AED spec'd my carb config specifically for my specs. It's pretty close, just the 2 issues I mentioned in my first post I would like to dial in tighter. If that's not possible without investment beyond basic jets/squirters/PV, then things are going to stay as they are until the FI.

I appreciate your help and the help of others on this thread, but we seem to be getting way more in the weeds that I am wanting to go just to address the 2 issues I asked about. I'm certainly not wishing to go the road of doing everything 100% from scratch as I view that as a waste of my time since I'm going FI.

Things are going to stay as they are and I'll use the o2 sensor to get the AFR in the ranges I'm happy with during the driving scenarios I'm looking to account for. Long as my engine is a bit happier and no damage occurs, that's fine to get me by until the FI.

[Bruce Meyer]

If your still having off idle hesitation, try a more aggressive pump cam. I found that more effective than going up in squirter size.

[92GTA]

Originally Posted by Bruce Meyer

If your still having off idle hesitation, try a more aggressive pump cam. I found that more effective than going up in squirter size.

Good tip, thanks!

[Formulajones]

I'm guessing you're still having off idle hesitation issues.

I didn't see any mention of what power valve you run in the front, but it's a player on tip in when transferring from the idle circuit to the main circuit as the vacuum reading will briefly dip, and with the idle transfer slot exposed enough on tip in, it will in fact use a bit of the power valve circuit until vacuum reading comes back up.

I've found that with a power valve too low, it creates a part throttle hesitation, and although I can tune most of it out with pump shot size and duration, it never seems to completely go away on some engine combinations. Sometimes it does, sometimes it doesn't.
So if you've tried various squirter sizes and squirter cams and still find a flat spot off idle, you'll need to jump up on power valve.

I had one recently that part throttle stumble simply would not disappear with any amount of squirter tuning. I moved the power valve up to 6.5 from 4.5 and it completely disappeared. Some holley carbs simply have trouble with that transition from idle to main circuits and need a little PV help.

[92GTA]

Originally Posted by Formulajones

I'm guessing you're still having off idle hesitation issues.

I didn't see any mention of what power valve you run in the front, but it's a player on tip in when transferring from the idle circuit to the main circuit as the vacuum reading will briefly dip, and with the idle transfer slot exposed enough on tip in, it will in fact use a bit of the power valve circuit until vacuum reading comes back up.

I've found that with a power valve too low, it creates a part throttle hesitation, and although I can tune most of it out with pump shot size and duration, it never seems to completely go away on some engine combinations. Sometimes it does, sometimes it doesn't.
So if you've tried various squirter sizes and squirter cams and still find a flat spot off idle, you'll need to jump up on power valve.

I had one recently that part throttle stumble simply would not disappear with any amount of squirter tuning. I moved the power valve up to 6.5 from 4.5 and it completely disappeared. Some holley carbs simply have trouble with that transition from idle to main circuits and need a little PV help.

It's a 4.5. Thanks, I'll keep that in mind. I was thinking of trying a 6.5

[Formulajones]

Yep 6.5 will most likely cover it. I've found 4.5's in some holleys just don't do it.

I tried that 4.5 in our Z and spent a week of driving tuning the squirter circuit all over the place. Just could never get the flat spot out completely, and it was a real nuisance being a 4 speed car when you're on and off the gas all the time shifting.
Went back to the 6.5 which is actually the factory PV for this application, and not only did the flat spot off idle and low speed completely go away, but part throttle response also picked up and became much more crisp.

The AFR gauge would show the car actually running a bit rich in this configuration so we can't always pay attention to the numbers when drivability is the main concern. But a little rich is okay, especially with todays fuels, and the car still returns excellent MPG.

[92GTA]

Originally Posted by Formulajones

Yep 6.5 will most likely cover it. I've found 4.5's in some holleys just don't do it.

I tried that 4.5 in our Z and spent a week of driving tuning the squirter circuit all over the place. Just could never get the flat spot out completely, and it was a real nuisance being a 4 speed car when you're on and off the gas all the time shifting.
Went back to the 6.5 which is actually the factory PV for this application, and not only did the flat spot off idle and low speed completely go away, but part throttle response also picked up and became much more crisp.

Awesome, I'll try that, then the cam, then a larger squirter in that order.

[Formula jg]

I understand you are just filling in the gap between now and EFI so I will not get to deep into this tuning. I still believe if you have a non-filter top type air cleaner lid you should use it to eliminate that as a contributing factor to the hesitation your getting. Have you had a chance to verify the primary transfer slots are approx. square in size? Secondaries can be closed for starters and set the idle speed with those as mentioned by another member.

[92GTA]

Originally Posted by Formula jg

I understand you are just filling in the gap between now and EFI so I will not get to deep into this tuning. I still believe if you have a non-filter top type air cleaner lid you should use it to eliminate that as a contributing factor to the hesitation your getting. Have you had a chance to verify the primary transfer slots are approx. square in size? Secondaries can be closed for starters and set the idle speed with those as mentioned by another member.

I haven't called AED yet. I got caught up in doing a new starter and a couple other projects. My o2 sensor/gauge showed up yesterday and I'll head over to an exhaust shop to weld in the bung by the end of the week.


I'll post back soon as I speak to AED.


Thanks!

[92GTA]

I'm waiting on a return phone call from a tech guy at AED, but in the meantime here is some more info I've gathered now that my AFR gauge is installed:

I redialed in my 4 corner idle screws and they were right exactly where they needed to be already after trying a 1/8 turn richer and leaner. Now that I have an IR temp gun tho, I noticed the header tube primaries were a tad hotter on the passenger side so I moved out the 2 idle screws on that side 1/8 to richin that side up a tiny bit. Now everything is spot on.

12.2 AFR @ idle in park. 9.7 inches of ported vacuum.
12.4 AFR @ idle in Drive. 7.5 inches of ported vacuum. (Looks like I should stick with my 4.5 PV and not go to a 6.5, correct?)

Attempting to go even the slightest bit leaner resulted in a loss of 2-3 inches of vacuum so I'm happy with the 12.2/12.4 @ idle.


13.8-14.2 AFR under light acceleration.
14.8-15.2 AFR under moderate acceleration.
Drops down to ~13.4 AFR as the secondaries open up under heavy acceleration.

Being as lean as things are I did not want to attempt any aggressive/full acceleration runs.


So I for sure need to go up a few jet sizes on my primaries, if I'm a 72 now what do you think, a 76 or 78?

When AED calls me back I'll ask the primary transfer slot size and get their take on how many jet sizes go up and where to start with my stumble upon moderate to aggressive acceleration from a stop (PV, squirter, or pump cam).

[Formulajones]

Light acceleration AFR's look fine, nothing to worry about.

The moderate acceleration AFR's are going leaner because of the 4.5 power valve, it's not opening with moderate throttle.

Still need to go with the 6.5 power valve, that'll help the moderate acceleration AFR's and keep things in a safe area, especially if the engine is pushing the pump gas limit.

On the primary side, You are better off going up on the power valve than you are going up on jet. If you just go up on jet it affects the AFR everywhere so you lose fuel economy. Since your light throttle AFR's are fine around 14.0 I'd leave it. That's perfect stoich for todays 10% ethanol.
Just go up on power valve so you can richen the moderate throttle area of the curve. That way during light throttle steady cruise you get your 14.0 AFR and better overall fuel mileage, yet tip into the throttle a bit, vacuum drops, power valve opens, and it should help to bring your AFRs down in the moderate acceleration area where it's needed.

Your stumble from a stop is still power valve related, trust me. Swap the 6.5 in there and you'll fix both issues with one part....done. No need to wait for a phone call wondering what to do.

[Tom Vaught]

Originally Posted by Formulajones

Light acceleration AFR's look fine, nothing to worry about.

The moderate acceleration AFR's are going leaner because of the 4.5 power valve, it's not opening with moderate throttle.

Still need to go with the 6.5 power valve, that'll help the moderate acceleration AFR's and keep things in a safe area, especially if the engine is pushing the pump gas limit.

On the primary side, You are better off going up on the power valve than you are going up on jet. If you just go up on jet it affects the AFR everywhere so you lose fuel economy. Since your light throttle AFR's are fine around 14.0 I'd leave it. That's perfect stoich for todays 10% ethanol.
Just go up on power valve so you can richen the moderate throttle area of the curve. That way during light throttle steady cruise you get your 14.0 AFR and better overall fuel mileage, yet tip into the throttle a bit, vacuum drops, power valve opens, and it should help to bring your AFRs down in the moderate acceleration area where it's needed.

Your stumble from a stop is still power valve related, trust me. Swap the 6.5 in there and you'll fix both issues with one part....done. No need to wait for a phone call wondering what to do.

Best advice I have seen written in a good while.

The Power Valve, even if it is blown, does not affect the idle circuit.
If the Main Circuit is "Off" then how can the Power Valve do anything to the idle of the vehicle. Holley Engineers put the 6.5" Power Valve in the carbs for a reason.
A heavy vehicle might even like a 8.5" power Valve to help with the immediate high load when you try to accelerate the vehicle.

The Thermal Guns do a pretty good job on the temps in the exhaust headers. Not as good as thermo-couples in the pipes themselves but a lot cleaner vehicle without that thermal hardware. Ok on the dyno though.

Tom V.

[92GTA]

AED called back and suggested I need to close my rear throttle blades more for a 70/30 to a 80/20 front-rear bias. Then readjust my idle and start with my 4 corner idle screws at 1.5 turns then find where the engine is happy from there. They said I shouldn't need a PV change and this could correct my light acceleration/cruising AFRs. He said to not depend on my AFR gauge for anything below 1,500, especially with my camshaft. He also suggested going from the pink to the red on the plastic pump cam. Although I'm sure I'm already running the red and need to go to the orange. He said my IFR is non-adjustable and couldn't say what size it was but it's at the 11 and 1 o'clock positions in the block.

It sounds like I'll follow their advice and then see how it goes. From there I'll consider if I need to still swap the PV as suggested.

Thanks!!!

EDIT: Almost forgot, he said he wanted to see me bump my base timing from 12-14 to 16 or maybe even 18. I might be 16 a try but 18? hmmm....

[ta man]

AED suggests 1.5 turns out on a four corner that seems like alot? Where are yours set currently.

[92GTA]

Originally Posted by ta man

AED suggests 1.5 turns out on a four corner that seems like alot? Where are yours set currently.

Well, the guy said 1 to 1.5 turns out.


I'm not sure to be honest, I just have them set where I thought it was happy and didn't keep track.



As I seat them back in, I'll take note of how far I had them out just for my knowledge.

[Formulajones]

Originally Posted by 92GTA

AED called back and suggested I need to close my rear throttle blades more for a 70/30 to a 80/20 front-rear bias. Then readjust my idle and start with my 4 corner idle screws at 1.5 turns then find where the engine is happy from there. They said I shouldn't need a PV change and this could correct my light acceleration/cruising AFRs. He said to not depend on my AFR gauge for anything below 1,500, especially with my camshaft. He also suggested going from the pink to the red on the plastic pump cam. Although I'm sure I'm already running the red and need to go to the orange. He said my IFR is non-adjustable and couldn't say what size it was but it's at the 11 and 1 o'clock positions in the block.

It sounds like I'll follow their advice and then see how it goes. From there I'll consider if I need to still swap the PV as suggested.

Thanks!!!

EDIT: Almost forgot, he said he wanted to see me bump my base timing from 12-14 to 16 or maybe even 18. I might be 16 a try but 18? hmmm....

He's partially correct but his approach not so much.

You already stated your idle AFR's are in the mid 12's, that's fairly rich but most engines with a lot of overlap will end up in that area to be happy, so not unusual. Running the mixture screws out 1.5 turns is pretty far when you have 4 of them, and richening that circuit to try and compensate for an off idle drivability problem isn't the best approach. Your idle AFR's are already rich enough, going further is going to cause other issues.
All richening the idle circuit will do is richen your AFR's across the board in unison and is not the way to correct your light acceleration cruising AFR's.

Like I said, nothing wrong with the light cruise AFR, it's the moderate throttle AFR that goes a bit lean because the power valve isn't opening. Fattening up the idle mixture isn't the way to fix this. It adds fuel "everywhere" so It'll screw up your light throttle cruise AFR and in essence decrease your fuel mileage as a result, not to mention just make your idle AFR even fatter and likely start blackening the plugs.

Pink is the most aggressive pump cam so don't know why he's telling you to go red. The pink works in nearly every single application I do here if you run the right squirter size.

That power valve affects your off idle tip in more than people think.

Think of it this way. When you open the throttle blades you're creating a big hole that sucks air. That hole has to be filled with fuel to mix with that air.
As those blades open you're exposing the idle transfer slot which activates the main circuit (think jets) but it also activates that power valve IF the vacuum level drops low enough. If the vacuum level doesn't drop low enough, then you're relying solely on the jet size and the squirter size to cover that hole. Sometimes that isn't enough and you need that power valve to open for a brief moment to make up the difference until the vacuum comes up. Going really big on the squirter trying to cover that hole is kind of a double edge sword. Might be able to get it done that way but now every time you move the throttle it's dumping that large amount of fuel even at high vacuum levels where it's really not needed (think wasted fuel). Again it gets into that fuel mileage thing and efficiency. That's why you're better off attacking this from the power valve standpoint.

No worries of the power valve opening at idle....it doesn't work that way. With the blades adjusted properly the main circuit is shut off at idle, so jets as well as the power valve are inop.....no matter what the vacuum reading is.

On the initial timing thing, he's somewhat in the ballpark but that's not really your issue. yes you can run as much as 18 initial timing but I rarely find that needed in most applications. Again there are a lot of variables at play to determine that and without the car in front of me it's impossible for me to make any suggestions with so many unknowns. Would take a book to explain.

[Tom Vaught]

The old two corner idle circuits needed 1.5 turns out to achieve a proper idle fuel mixture on engines in the 427 to 454 size range in the old days.

When we went to 4 corner idle we were now dividing the same fuel requirement by 4 so the turns out was 3/4 turns out for each 4 corner idle screw. Maybe 1 turn out on a big camshaft engine.

If the tech does not know what the idle feed restrictions are sized at, what carb did he sell you?

.038" is a normal 850 cfm #4781 carb Idle Feed Restriction size.

Measure and see what you have.

Tom V.

[4zpeed]

Just in case you didn't know 92GTA, there is a excellent sticky (SOME HOLLEY TUNING TIPS) by Tom Vaught in the (TECH THREAD ARCHIVE).

http://forums.maxperformanceinc.com/...d.php?t=811891

It may be of some help currently or in the future with any issues you may further encounter.


Frank