Holley/Fod 94 Carb Adjustment

Gene F

Gene F

Well-known member
Have a Holley 94 on to of a V-8. The thing seems to be loading up a bit at idle. A slight black coming out tailpipes. If it is hot outside the thing slows down so much at idle after you sit at a traffic light that it will eventually die. Carb was regasketed recently, and ran great.

I pulled the low resistance air filter off, and blew it out, it seems fine (same with it off). So if I turn the idle air adjustment screws in to just touch their seat, how many turns out should I start with my adjustements? Turning them in goes rich, or lean?

How do I test my power valve, if it comes to that? I have a mighty-vac gun, so I could test my manifold vac (no port on the carb).
 
I had a similar problem and I readjusted my float setting to 1.5” and it now idles perfect. What probably was happening is the fuel level in the bowl was to high and with the carb getting heat soaked the fuel is percolating into the Venturi and down into the engine thus causing the engine to overload and shut off. This also causes a hard start. A leaking power valve can also cause a problem. Good luck.
 
I just changed my float setting. I figured it was worth a shot. It is better. I did not go 1.5", but maybe I might increase it a bit. after I get the air fuel screws in the ballpark. As soon as I started it back up, within about 10 seconds it started idling higher, and better. Might be on-to something with the float thing.
 
Attach a vacuum gauge to the intake manifold and adjust the two air screws to get the highest reading on the gauge and you should be good to go.
 
The tail pipes are still throwing a cast of black smoke, and still mildly loads up. Needle screws are only 1 turn off their seat. I am going to order a power valve. I think the diaphram is torn... I have a couple of used one, but if I am going to do it, I only want to do it once. Not like I need the car to get to work.
 

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Power valves can be a problem on the old 94s. The new types don't fit well. One of our former barn fellows has a fix. Charlie Schwendler makes them work. His info can be found in a Google search. In muliples, only the one should have a power valve.
 
Those tiny paper air filter can be restrictive. I had a new one that would change the idle when I put it on. I thought, how much can that piece of junk be restricting it driving it down the road. I switched the air filter design.

To adjust the carb make sure the float level is correct. At operating temperature gently close the idle mixture screws in and then back them out 1 1/2 turns. When they are turned in all the way the engine should die. The idle mixture screws are the only place it should be getting fuel at idle. If it still runs you have something else leaking fuel into the engine, maybe a power valve... If turning the screws in all the way did starve it for fuel, then back them out to around 1 1/2 turns. It just a starting point I use on all carbs. Then what I like to do is take a propane enrichment tool which is just a can of propane with a valve on the end of it. I open it just a little bit and pass it over the carb, if the idle goes up the engine wants more fuel and I open the screws a bit more. If the idle goes down, it's already too rich and I turn the screws in a little. When I have both screws adjusted the "same, both turned out exactly the same amount the propane doesn't do anything. Then I know I'm pretty arm close to having it set right. Now that's just setting the idle there are lots more things to tune on a carb.

I was smog tech for the State of CA. They wanted us to use the propane enrichment tool. What they wanted was you to adjust the carb to the lean side so that when you added the propane the idle came up 50 rpm. That's doesn't make the smoothest running engine at idle. It's a great tool for looking for vacuum leaks or adjusting air fuel mixture. You can do the same thing with a little spray of carb cleaner.
 
I was always taught to adjust idle screw(s) until engine starts to stumble, then back off a half turn. Been doing that for past 70 years.
 
The power valve is coming from Vintage Speed. I have never gotten a part from them that I am dissatisfid with. I am sure they will send the correct part for the carb. That carb has it's own parts sheet, so the power valve should go with that carb. (6.5, but I ordered an 8 too - my vac is 16 - 15ish.)

I already have the lifetime low resistance element. They have advised me on how to clean it.
 
All fixed. New 7.5hg power valve I got from Vintage Speed did the trick.

BTW, when I took the air horn casting off of the primary carb, the bowl was about 99% dry. Evidently it was leaking through allowing the fuel to run into the intake l
 
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Vacuum fully warmed up is: 20-21, and the needle is not jumping around. In drive between 16-16 1/2 and the needle is steady.

Good enough for power brakes if I so ever choose. (Source; LEEDS brakes tech).

The idle did pick up and smmoth out a bit.

Thanks guys.
 
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