Holley whine/whistle

[Bradley D.]

I have recently purchased a 67 L79 (327/350) and have expeienced a whine or whistle once the engine is heated up.
Wife will notice it before I can hear it, but it is quite noticable. I have isolated it to the carb. I have replaced the carb to manifold gasket and no difference. Both carb and manifold surfaces are not warped. Car runs fine with no detectable performance issues.

Am I in need of a total carb rebuild or is there something else I can check or do?

[Clem Z.]

Re: Holley whine/whistle

are you using the correct gasket between the carb and intake. using the incorrect shape gasket will cause the whistle.

[Gene M.]

Re: Holley whine/whistle

What Clem says is important that the gasket opening matches the intake openings.

[Ralph S.]

Re: Holley whine/whistle

Hold your finger over the vent tubes for carb bowls while the engine is running and see if it stalls, i had that happen once and was a leaking power valve diaphram

[Bradley D.]

Re: Holley whine/whistle

Well I oredered it from Corvette Central for the 350/aluminium intake, the 300hp has a significantly different gasket arrangement. That is what I took off.

A four port top gasket, then a stanless baffle, then a large hole (0ne) on the bottom. I'm convinced that is wrong. Replacement is a three barrel (two primaries, one large on the secondaries)

No whistle when cold, but it does it continously on power and acceleration, not so much when coasting. But it does it at idle. I used a paper towel tube
to find the source. Seems more to thesecondary side, but I suspect the sound could be somewhat miss leading.

[Bradley D.]

Re: Holley whine/whistle

Hold your finger over the vent tubes for carb bowls while the engine is running and see if it stalls, i had that happen once and was a leaking power valve diaphram

I'll give this a try thanks.

[Jeff C.]

Re: Holley whine/whistle

Power valve

[Gerard F.]

Re: Holley whine/whistle

Brad,

Take a look at the second archived thread below, specifically #13 to the end.

The whistle could be caused by a mis-adjustment of the secondary throttle plate. On a 3810 and other holley's there is a small screw which adjusts the opening of the secondary throttle plate at idle.
Try wiggling the secondary throttle, or restricting the air flow to the secondary barrels, when it is whistling. See if it changes the whistle.
If it does, you found your problem.

[Bradley D.]

Re: Holley whine/whistle

Brad,

Take a look at the second archived thread below, specifically #13 to the end.

The whistle could be caused by a mis-adjustment of the secondary throttle plate. On a 3810 and other holley's there is a small screw which adjusts the opening of the secondary throttle plate at idle.
Try wiggling the secondary throttle, or restricting the air flow to the secondary barrels, when it is whistling. See if it changes the whistle.
If it does, you found your problem.

What I did was to put a very small amount of grease on the secondary plates, and that did not change anything. I will try your suggestion later today, as I've got another option to drive from an earlier post. Car has to be good and hot/warm befor it happens. Maybe about 20 miles or so, but thanks for the input.

[Bradley D.]

Re: Holley whine/whistle

Well I tryed:
Hold your finger over the vent tubes for carb bowls while the engine is running and see if it stalls, i had that happen once and was a leaking power valve diaphram
No change, nothing.
and:
Try wiggling the secondary throttle, or restricting the air flow to the secondary barrels, when it is whistling. See if it changes the whistle.
If it does, you found your problem.
Again, no change.
and:
More carb cleaner in more places, plus some old places again.

I'm leaning to a carb rebuild at least, but not convinced that will fix it, but think that is worth it first before I send it out for a complete rebuild.
Any other ideas?

[Frank E.]

Re: Holley whine/whistle

I had the same problem on time. As it turned out, the bores of both the primary and secondary throttle shafts were the cause of the whistle. The solution was to rebuild and include a machining of the bores. For Holly's, I've always used Bob Kunz in St. Louis. Excellent work.....

[Gerard F.]

Re: Holley whine/whistle

Brad,

If your carb is an original 3810 and never been rebuilt, maybe it is time.

You can try pulling the carb, adjusting the the secondary butterflies. Adjust the screw on the bottom so that the secondaries are fully closed, then adjust the screw 1/4 to 1/2 turn only to open the butterflies. Also while you have it off, tighten all the screws between the throttle plate and the main body.

If you still get the whistle, it is probably a vacuum leak between the main body and the throttle plate, or through the throttle shafts. You could have a warped main body or throttle plate. Holley's of that vintage are known for this, and you will probably have gas leaks on the sides of the carb to the manifold.

If you send it in for a rebuild, make sure they plane the base of the main body, and the throttle body. Also bush the throttle shafts. It might even be cheaper to just replace the throttle plate assembly.

I'm assuming that the carb is an original 3810, but you haven't confirmed that. They do wear out, and warpage of the potmetal parts is common.

[Bradley D.]

Re: Holley whine/whistle

Brad,

If your carb is an original 3810 and never been rebuilt, maybe it is time.

You can try pulling the carb, adjusting the the secondary butterflies. Adjust the screw on the bottom so that the secondaries are fully closed, then adjust the screw 1/4 to 1/2 turn only to open the butterflies. Also while you have it off, tighten all the screws between the throttle plate and the main body.

If you still get the whistle, it is probably a vacuum leak between the main body and the throttle plate, or through the throttle shafts. You could have a warped main body or throttle plate. Holley's of that vintage are known for this, and you will probably have gas leaks on the sides of the carb to the manifold.

If you send it in for a rebuild, make sure they plane the base of the main body, and the throttle body. Also bush the throttle shafts. It might even be cheaper to just replace the throttle plate assembly.

I'm assuming that the carb is an original 3810, but you haven't confirmed that. They do wear out, and warpage of the potmetal parts is common.

Carb has been rebuilt some time ago although not many miles. Previous owner had the work done. It sure looks like a 3810, but I don't know what to look for to be certain, i.e. numbers, codes, that type of thing. I did cover the secondaries and the whistle continued, and then the engine stalled.

[William F.]

Re: Holley whine/whistle

You've got the wrong carb to manifold gasket if it has a stainless plate. Correct is a 3 hole arrangement-gasket is one piece, somewhat thick, mabe 1/32 in and can see that it's composite. don't use the cheap thin 3 hole one supplied with some rebuild kits.

[John H.]

Re: Holley whine/whistle

It sure looks like a 3810, but I don't know what to look for to be certain, i.e. numbers, codes, that type of thing.

Brad -

Photo below shows the stampings on the front side of the choke air horn on a 3810 - yours should look the same, except the date code on the bottom line will be different.


3810AirHorn.jpg