Bad idle at leaner AFR with holley

67rcks · Feb 6, 2011

I can tune the idle up to 11.5-12 AFR (AEM wideband kit). Leaning it further causes white smoke. At 11.5-12 it has a healthy sound and no visible smoke. I was able to get up to 13 with idle screw just about 1/2 turn remaining to be fully seated; when fully seated engine stops (so power valve works).
My setup: 302 with mild cam, 650 cfm double pumper, engine at operating temperature.
Is it normal for holleys to run at richer AFR? Have you been able to run near stoich AFR at idle (14.1-14.5) with similar setup and have clean emissions?

j69302 · Feb 6, 2011

At idle you want to hook up a vacuum gauge and adjust the mixtures for highest vacuum.

If you dont have a vacuum gauge, you can use a tach or listen for the highest and smoothest RPM.

brianj5600 · Feb 6, 2011

More details on the cam, ignition timing and compression. All of those matter. Also how much of the transition slot is showing? It should look like a square when viewing from the bottom. Leaning the idle should not give you white smoke. Could it be steam from humidity? DP's are know for having large idle feed restrictors for use on more racy engines, but since you have control with the mixture screws you should be able to get idle right. It may need to be reduced for light throttle and cruise though. Here is a good write up on tuning a Holley. There is a pictures and description of idle/transfer circuits as well as pvcr, which can be usefull if you want to lean cruise. Carb Tunning

PoppyMod · Feb 7, 2011

67rcks said:
I can tune the idle up to 11.5-12 AFR (AEM wideband kit). Leaning it further causes white smoke. At 11.5-12 it has a healthy sound and no visible smoke. I was able to get up to 13 with idle screw just about 1/2 turn remaining to be fully seated; when fully seated engine stops (so power valve works).
My setup: 302 with mild cam, 650 cfm double pumper, engine at operating temperature.
Is it normal for holleys to run at richer AFR? Have you been able to run near stoich AFR at idle (14.1-14.5) with similar setup and have clean emissions?

Based on what you stated about your engine, you should be able to attain the stoic AFR, perhaps a little fatter (richer), if your engine likes it, but not, the 11-12 you're seeing. AT WOT, ideally, you will shoot for an AFR of low 13'ish and in a flat line to your max RPMs. But, either your "seat o-meter" or a dyno session will better tell, if your engine "likes" these settings. Also, your advance rate will affect it.
How much vac is your engine making at idle?

10secgoal · Feb 12, 2011

PoppyMod said:
Based on what you stated about your engine, you should be able to attain the stoic AFR,

What did he say that makes you say that ?
I don't think I've ever gotten a carb'd car to idle at stoich. Might be able to do it with a stick. But will more than likely surge at a light cruise. A cam and auto you can pretty much expect 12.5 to be what the engine will want, and have good tip in.

PoppyMod · Feb 12, 2011

10secgoal said:
What did he say that makes you say that ?
I don't think I've ever gotten a carb'd car to idle at stoich. Might be able to do it with a stick. But will more than likely surge at a light cruise. A cam and auto you can pretty much expect 12.5 to be what the engine will want, and have good tip in.

Hi

Based on what was in the engine (didn't appear to be all that radical) and it is tight (making good vacuum (15-22), adjusting those mix needles should allow the AFR at idle to arrive at the 14.5-8 ratio, and even shut the fuel supply off entirely. That is, if all other systems are operating as designed. If not, there's either a leak, poorly adjusted valves, incorrect timing, or a crazy wide duration cam bleeding off vac. causing a poor signal to the carb.

67rcks · Feb 21, 2011

Valves are timed 218° (intake duration) 228°(exhaust duration) at .005" (actual are 274/284 I guess), , some overlap, 0.471" valve lift. Intake opens at 0° ATDC and closes some 35° ABDC. This timing, and about 9:1 compression rate gives rather equal pressures 130 +-5 pounds among all cylinders when engine is cold; may be a litle bit higher because I used that silly gauge that you have to firmly hold with one hand while cranking the engine. I got 145 psi at cyl. no. 5 - there is the easiest access to it. Is this enough or do I need higher pressures?

67rcks · Feb 21, 2011

i also suspect coolant leak causing white smoke at near-stoich AFR. The engine does not go into rpm as easily as I would expect too, and is hard to start when parked overnight even during summer; it restarts easily then.

Last time I noticed a pressure in the upper radiator hose. Is it possible that hot coolant and water pump would make the hose as hard as a soft plastic pipe?

PoppyMod · Feb 21, 2011

67rcks said:
i also suspect coolant leak causing white smoke at near-stoich AFR. The engine does not go into rpm as easily as I would expect too, and is hard to start when parked overnight even during summer; it restarts easily then.

Last time I noticed a pressure in the upper radiator hose. Is it possible that hot coolant and water pump would make the hose as hard as a soft plastic pipe?

Bud,
With what you are now reporting, this is starting to sound like a head gasket leak. Noticing any coolant loss? Sounds like a combustion leak into the coolant and is being verified by the excess hose pressure. You might be able to verify it by adding a radiator pressure tester to the rad and letting the engine idle. One you may see excessive pressure and it may be pulsating, as well. Also, the coolant may showing bubbles or smell more like combustion gases than anti-freeze.
Also, any signs of oil contamination? Leaks can show up in two places, oil and coolant. Oil can be discolored with a brownish sludgy looking goop.
what does the engine vac reading tell you?

Bad idle at leaner AFR with holley

67rcks

Member

j69302

Active Member

brianj5600

Active Member

PoppyMod

Member

10secgoal

Active Member

PoppyMod

Member

67rcks

Member

67rcks

Member

PoppyMod

Member

Similar threads

Bad idle at leaner AFR with holley

Member

Active Member

Active Member

Member

Active Member

Member

Member

Member

Member

Similar threads

Privacy & Transparency

Privacy & Transparency