Another Holley whistle

[Robert S.]

Car is a 71 LT-1. The whistle just developed and is intermittent, and seems most noticable during conditions of high manifold vacuum.

It appears that the whistle is coming from the primary air horn (cupping my hand above the choke without blocking air muffles the sound).

I would think the whistle would be external to the carb if a leak at the carb base gasket or throttle shaft. Any ideas on this one?

[Clem Z.]

Re: Another Holley whistle

Car is a 71 LT-1. The whistle just developed and is intermittent, and seems most noticable during conditions of high manifold vacuum.

It appears that the whistle is coming from the primary air horn (cupping my hand above the choke without blocking air muffles the sound).

I would think the whistle would be external to the carb if a leak at the carb base gasket or throttle shaft. Any ideas on this one?

does the carb to manifold gasket match the manifold opening ???

[Robert S.]

Re: Another Holley whistle

Clem, the gasket is correct.

[Ronald L.]

Re: Another Holley whistle

Throttle shafts - search this forum, lots on this and I just got rid of my whistle today, among other problems by replacing the old carb with the restored original. Also there is a good set of video's on how to adjust the Holley's on u-tube but can't beat the advice here!

[Robert S.]

Re: Another Holley whistle

Ronald, my carb is a restored original. It does not have many miles on it since installed and just started the whistle today. I made no changes or adjustments prior.

Was your whistle noise coming from inside the primary air horn?

[Ralph S.]

Re: Another Holley whistle

Hold your finger over the primary vent tube while the car is idling, if the engine stalls i have found the power valve diaphram is leaking and needs to be replaced. The whistle is coming from the vent tube.

[Robert S.]

Re: Another Holley whistle

Thanks, Ralph. I did try plugging the primary vent tube with my finger as you mentioned, and it made no difference in the whistle (no change in the idle either).

[Ronald L.]

Re: Another Holley whistle

Yes, Noise was isolated with a hose.

If the power valve is blow, easy to do with one backfire, on Holley's prior to 1992, you can turn both adjusting screws in closed and the engine will not die. Check that, is it running rich?

Here is one link...http://www.bob2000.com/carb.htm

[Robert S.]

Re: Another Holley whistle

Ronald, power valve is not blown. Idle mixture screws will stall enigne when turned in.

Engine runs and idles without problems.

[Ronald L.]

Re: Another Holley whistle

Need to talk to whom ever did the restoration relative to bushing the throttle shaft. Did bush it due to wear?

[Robert S.]

Re: Another Holley whistle

I do not know the details of the rebuild. I'll probably pull the carb and look at the throttle shaft since it seems to be the most likely cause based on your comments.

[Robert S.]

Re: Another Holley whistle

I wanted to follow up and let everyone know that I THINK I found the problem. I pulled the carb off this morning and I noticed that the large screws on the bottom that attach the throttle plate to the main body were somewhat loose. I did not see any other problems, so I snugged those up and reinstalled the carb.

I then went and drove the car quite a bit and have not yet heard the whistle.

[Clem Z.]

Re: Another Holley whistle

I wanted to follow up and let everyone know that I THINK I found the problem. I pulled the carb off this morning and I noticed that the large screws on the bottom that attach the throttle plate to the main body were somewhat loose. I did not see any other problems, so I snugged those up and reinstalled the carb.

I then went and drove the car quite a bit and have not yet heard the whistle.

i would cross that carb rebuilder off of your list.

[Gerard F.]

Re: Another Holley whistle

i would cross that carb rebuilder off of your list.

I agree Clem,

If one of those screws fell into the intake manifold on one of those full open intakes, it would have really raised havoc. The restorer should have used some Loctite.

[Clem Z.]

Re: Another Holley whistle

I agree Clem,

If one of those screws fell into the intake manifold on one of those full open intakes, it would have really raised havoc. The restorer should have used some Loctite.

i believe that is why GM holley carbs do not have the center 2 baseplate screws like the holley factory carb do because they can fall into the intake if they get loose