Holley Expert Please

[Glenn B.]

I have a 67 427-390 with the correct 3811 carb. When I bought the car last year it had a number of obvious carburetion problems (choke didn't work, poor idle, very hard to start when hot, vacuum leak, etc). Over the winter I did a complete rebuilt on the carb. All is now well - except I still have a vacuum leak (whistle) when the engine is fully warmed up.

I spent an hour trouble shooting today - presuming the problem was the carb to intake or carb body to baseplate seal. I sprayed carb cleaner along both seals to no avail, also tried the throttle shafts.

I then began to get desperate and tried many things, I ultimately found I could completely and consistently eliminate the whistle by placing two fingers along across the secondary air horns (blocking most of the opening - but definitely not sealing it.

Can anybody tell me what the heck my problem is and how to fix it?

Thanks

[Gerard F.]

Re: Holley Expert Please

Glenn,

I'm not an expert at this, but I would suspect the at-idle position of the secondary throttle butterflies, either they are too far open or too far closed(probably too far open if you can stop the whistling with you fingers). Try moving the vacuum secondary rod when it is whistling to see if the movement of the butterflies corrects the problem. Unfortunately, the stop screw on a 3811 for the secondary throttle is on the underside of the base plate.

Also, maybe a mixture adjustment might do it.

Maybe Clem will chime in on this, he's the expert.

Jerry Fuccillo
#42179

[Glenn B.]

Re: Holley Expert Please

Hi Jerry:

The secondary idle stop too far open sounds like a reasonable possibility to me - thank you. I think I am at the point of not seeing the forest for the trees. I didn't touch the idle stop during rebuild - but of course this problem existed before.

I will give this idea a go and let you know.

[Mark #28455]

idle plate adjustment

On the primary side, if more than about .030" of the off idle transfer slot is visible below the throttle butterfly, your engine will run too rich at idle. It was common practice in engines that were modified to a higher idle to drill holes in the primary butterflies to allow the extra air in (but definitely the BUBBA way to go). The correct way was to use the secondary idle stop to allow some of the air to come through the secondary side. If a prior owner had a radical cam, this may have been done before you ever got the car. For my BB engines, I purchased a tiny flat blade screwdriver set at the hardware store junk tool bin (it's only about 2" long total) and I can now adjust the secondary idle screw on the car - see if you can access the screw on your car.

Mark

[Clem Z.]

you can tweek the scondary throttle stop

buy bending the arm on the stop that touches the adjustment screw with a pair of pliers. just open the secondary by hand and bend away. i did it all the time so i did not have to remove the carb.

[Glenn B.]

The culprit remains at large...

Well, the secondary idle stop seemed like a good bet - but regretably doesn't seem to be the answer.

I managed to find a very small slotted screwdriver in a $4 "Stubby" multi-bit I have on hand to change the batteries in my kids toys. Adjusted the butterflies to be as close as parallel as I could eyeball to the baseplate. Drove it in to work today - thought the choke was hung up, car now won't idle below 1500 RPM. The secondaries are partially open now (put my hand over air horn and idle drops back).

Anyhow - after 20+ minuts of running, I STILL get the vacuum leak whistle even though the secondaries are partially open! - so it just doesn't seem that the idle stop can be the problem.

Is there a carburation equivalent to Gus Grissom out there? I really wish I could find a local mechanic that really knew Holley carbs. Any additional suggestions much appreciated.