Holley 750 not maintaining Idle after installing fuel pressure gauage

[AM.MSCL]

Sorry for the long thread but I am trying to figure out what happened after adding a Fuel Pressure gauge inline to the carb on my engine.
I have been communicating with Holley but was hoping someone here might have some ideas also to what could be going on.

The Holley is a 750 Vac 2ndariers with electric choke.
The Engine is a YC 400 in my 69 Firebird. More info that I know below along with the issues.
thanks for the time to read and reply.

I sent to Holley:

I added a inline fuel pressure gauge on Friday morning and at idle I am reading 5-7 lbs with the engine warm. When I dry rev (rev in neutral) the motor to any rpm level the fuel pressure goes to a flat 5 lbs.
I do not know the Cam Specs or the Compression ratio as the engine was built prior to me owning the vehicle.
I do know the cam is a little bigger then stock as I can hear a lope at idle. The pistons are SealedPower .30 over and there is a double chain timing chain.
I have no clue if any head work was ever done but the I do know the rockers are stock looking stamped 1.5.
Edlebrock intake with MSD Distributor with 12 degrees of timing.
1) Issue prior to adding the fuel pressure gauge is: sitting at idle at a stop light, take off full throttle and let off the throttle and push in the clutch the engine dies. If I shift into 2nd it does not happen. Both cases taking the RPMs up to 3000 or 4000+. Cruising in 2nd or 3rd gear doing about 1500 RPMs and go full throttle up to 4000+ RPMs and let off the throttle and push in the clutch; the engine keeps running.
2) Drove the car Friday after adding the fuel pressure gauge no new issue. Saturday morning took the car out and outside temp was 20 degress cooler then Friday. Choke worked great and after engine was warmed up I got full throttle a time or 2 up to about 4000 RPMs. Pulled into drive thru and push in the clutch and engine finds idle of 750-800. Within 5 seconds of finding idle she slowly drops idle and dies. Keeps doing this unless I keep reving the motor. Get home let sit for 4-5 hours (outside temp 5 degree increase maybe); start car choke not acting like it wants to work and engine finds idle at 750-800 then within 5 seconds slowly drops idle and dies.
3) Looking at carb to maybe find reason for #2 I see what appears to be fuel stain on the intake at carb base on driver side. Area was clean prior to the issue in #2

Holley's 1st Response:
Hello,
Thank you for contacting Holley Performance Products. It actually sounds like your fuel is bowling inside of the bowl at low RPM or idle. This is commonly referred to as percolation. When the fuel is stationary in the bowl, so an idle condition the temperature in the bowl rises, modern ethanol based fuels have a lower bowling point than a non ethanol based fuel. Unfortunately there isn''t many options we currently have to help reduce the internal temperature. One of the few options we do have is to use a phenolic spacer between your carburetor and intake manifold, this will help reduce the heat transfer from the metal surfaces.

Me:
Is that the possible cause for number 2 also?
Because the day this happened it was actually cooler than it has been all summer long in Austin, TX.
Is 5psi enough for this carb setup also?

Holley:
Yes, the temperature in the engine bay, around your fuel link, and more importantly between the fuel bowl and your intake manifold is more important than the atmospheric temperature. The bowl is getting hot from the radiant heat off of your cylinder heads and intake.
5-7 PSI is what we commonly recommend.

Me:
Could a vacuum leak from a bad gasket between the carb and intake cause the problem with finding idle then a few seconds later slowly dies?
Also is 5 psi good for full throttle? Not that I am full throttle all the time but occasionally I do.

Holley:
It could yes, but it would more commonly cause your rpm at idle to be high or uncontrollable. 5Psi @ WOT could pose a problem over a period of time. Typically at WOT you want 5.5-7 PSI, mechanical pumps can be difficult to regulate to .5 psi, do you know the part number to your fuel pump and are you running a regulator?

Me:
I am currently running a stock fuel pump or stock parts store replacement pump, from the way it looks; there are no markings on it to indicate that it is an aftermarket performance pump.
I am not sure what a stock Pontiac 400 pump should be able to supply psi wise.
I have no regulator in the fuel system.

Holley:
Typically if you have concern with your fuel bowls running dry at high RPM ranges, I would recommend installed at least a regulator on the system 6psi Is the ideal fuel pressure reading.

My latest information to Holley:
This weekend I swapped out the carb to intake gasket and also added the edelbrock 2732 square bore to spread bore adapter plate. I have a performer intake.
First start of the car in a week and it starts immediately finds idle and dies. This continued for 2 more attempts. I then decide to adjust the fast idle to speed up the idle and finally got the engine to keep running but idle was at 2000 Rpms, I immediately adjust it back down to 800 and then blip the throttle and it dies. Start it again and tries to find idle at 600 and dies. I turn fast idle in about 1/4 turn and start engine again and idle is 1300 rpm, I blip the throttle again and it dies.
The engine never had time to even warm up any and the problem keeps happening; what other problem do I need to look at other then the fuel boiling in the bowls?
Thank you

Holley's latest response:
It sounds like there is a blockage in the idle circuit of your base plate or metering block. If you remove the carb from the intake, the small holes below the throttle plate are your idle fuel passage ways. I would suggest thoroughly cleaning all of the idle circuit. If your fuel pressure is correct and there isn't an issue with your pump, I would think that you are running out of fuel delivery at idle. I would also check the idle air bleeds, which are the outside air bleeds behind your boosters in the venturii.

[AM.MSCL]

I guess maybe I should mention that the car had been running just fine for 2 years with the exception of issue number 1.
I current have 10 degrees of timing which is the max I could do without introducing lifter clatter at high rpms.
If I remember correctly I had 15 units of vacuum when I tuned it.

[Sieg]

Sounds like the issue started with installation of the pressure gauge.

Did you use teflon tape or some type of thread sealant that could have clogged a passage in the carb?

Has E10 fuel sat in the carb for an extended period?

Could the gauge be restrictive/defective?

Fuel pump possibly giving up? I just had a mechanical pump start to fail in the middle of resolving idle issues.

10*-12* initial timing should be fine and 32*-36* total timing.

The idle transfer slots in the venturi's should be set to expose .020" for a baseline.

Idle mixture screws are usually in the .75 to 1.50 turns out range.

The way it's seeking a high idle then falling off means it "could" be lean. Vacuum leak or idle mixture setting and/or butterfly transfer slot relationship.

Accelerator pump linkage should have a .010"-.015" play also. Too tight and the pump can weep fuel into the idle mixture.

All these settings should get you close......but if a circuit is experiencing blockage or there's a vacuum leak or fuel supply issue you'll have issues.

[GregWeld]

Call Eric - he's there in Austin.



He's on this forum… and also Carbuff is there as well as Gerno… They can point you how to get hold of Eric.


Go to this thread - find the guys and PM 'em if you don't know them.


https://lateral-g.net/forums/showthread.php4?t=29609