Thread: Running too rich - won't lean out

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I have a holley 750 on my chevy 383 stroker. its running too rich (lots of gray smoke) and will not lean out with the carb adjustments. Wondering if a carb rebuild will help?

Thanks

Are we there yet??
sorry Denny. Lol

Originally posted by DennyW
How much manifold vacuum do you have ? Are you running a oversize cam ? Do you have any vacuum leaks ? Has it backfired ? Did this just happen ? Do you have a anti-backfire valve installed in the carb ? Are your float levels ok ? Is your pump pressure to high ? Are you running a fuel filter ?

Its has an oversize cam. There doesnt appear to be any vacuum leaks. It has not backfired. it has been this way for a while (months). i dont think i have an "anti backfire" valve installed. Float levels seem Ok. I am not sure about the pump pressure and i do not have an inline fuel filter.

Does that help?

it happens more when cold, but still happens when warm. i recently cleaned out the fuel filter in the carb. but the problem continued.

thanks

How about drilling a couple of small holes in the primary throtlle plates. I'm sure you know more about that than I do Denny. I remember reading about that somewhere, but i don't remember the techique.

well - i ordered the rebuild kit, and will give the rebuild a shot.

Thanks

When you have it apart, use a straightedge and check the surface of the main body where the four screws hold the float chamber and metering plate on. If this surface warps from overtightening the screws, fuel leaks directly into the vacuum passage to the metering valve, causing rich running. It's easy to file the surface flat.

Wow- Thanks guys for the input.

I am going to start the rebuild today. To make matter worse, I just realized fuel has been leaking out where the fuel hose connects to the carb. Hopefully after the rebuild it stops leaking when i reconnect it.

maybe there is a block building up a the fuel filter on the carb.

Anyway - thanks for the help..

Originally posted by 71Demon
Denny above said check your power valve. A back fire usally blows them, if they don't have the protectors. If the idle air screws (actually fuel screws) don't shut the engine off when you run them in all the way in, then it is blown. That is the easiest check for a bad power valve.

Now to set them correctly take them out to between 1 and 1.5 turns from home. This is where the should be. As you run them in and out, the rpms should rise and fall as you go rich and lean. You want them set where the rpms peak, and that should be between 1 to 1.5 turns. If it is not, and you can shut the engine off by running them all the way in and stopping the fuel flow, then you have a working power valve, but on that is the wrong size.

If the peak is under 1.0 turn, then the power valve is too large, if it is greater than 1.5 turns then the power valve is two small.



You don't need to drill holes in the throttle plates. There is an adjustment for that. It is not easy to do buy it is there, and you don't have to buy new throttle plates if you drill holes two big.

If you look at the underside of the carb, you will see two slots in the bores for the primary, at idle you should have 0.020 of an inch of those slots exposed for the idle air circuts to operate correctly.

If the engine doesn't have enough air to idle at that setting, then don't drill holes in the primary plates use the adjustment. If you look at the underside on the secondaries, you will see an adjustment screw. That screw is for adjusting the air flow on the secondaries at idle. That is so you can get the front set with the .020 exposed, and still get the right airflow for idle.

Hopefully that will help you get it tuned in a little better.

Gary

I got the carb rebuilt, its still running rich. the only way i can lean it out is if i turn the fuel screws 1/4 turn from fully shut. are you saying that this indicates that i need a new power valve? i

Thanks

Originally posted by 71Demon
Sounds like it. The Power Valve is dumping in to much fuel, and your using the idle screw to lean it out. Your only slightly out of range, so the power valve is close to being the right size.

Now did the RPM's peak as I explained at that setting, and fall off either side of it. Could you stall the motor by running them all the way in?

Yes the RPMs peak and then fall off on the extremes. The motor did stall by closing alll the way.

I'm not familiar with Holley carbs, but why not mess around with the metering rods and metering jets? I've only messed with Edelbrock carbs.

Holley's use power valves and jets to accomplish what Edelbrock/Carter's do with metering rods and jets.

Originally posted by C9x
Holley's use power valves and jets to accomplish what Edelbrock/Carter's do with metering rods and jets.

Ahh, ok.