Geralds57

I’m working on a 67 427 with a factory Holley carburetor that whistles from a vacuum leak somewhere down inside the throat of the carb. It only happens after the engine gets hot. I’ve changed the carb to intake gasket twice, but no help obviously. It’s definitely down in the throat where it’s sucking air. Anybody had this problem?

JohnZ

Common Holley issue - first check the phillips-head screws that attach the baseplate to the bottom of the main body.

Geralds57

Thanks John. I’ll pull the carb tomorrow and check. So it’s sucking air between the base and the body?

DansYellow66

I had a Miopar 440 whistle once with a 4-hole intake manifold on which I used a single large hole carb gasket. Apparently the air moving past that open space or exchanging between bores would create the whistle. Installing a proper 4-hole carb gasket solved it.

R66

Put a straight edge across the baseplate corner to corner to check the flatness. I would guess more than half of the baseplates on used Holley carbs in my collection have warped baseplates from over tightening by BUBBA. A couple, I picked up free because BUBBA cracked the ear on one corner when over tightening.
I spent more than a day with sandpaper on a sheet of glass to flatten the base plate on our 3367.
Some people blame it on throttle shaft wear, but I have never had one bad enough to cause a real bad vacuum leak or whistle..

Also had a squealing noise off idle when I used a 4 hole gasket on an Eldebrock C3B 3 hole intake when I installed a 4 hole gasket under the carb.

Sleper

the other thing you can try is when it is making noice use a propane torch to find the leak. the rpm will raise when you get close to the leak. it will prove it is not a warped base or another leak somewhere else. Eliminating all other areas. Good luck

tbarb

If the Holley is original to your car the best $$ you can spend is to have the main body, (front, back and bottom) along with the throttle body, (top and bottom) milled by a good machine shop.

While you have the throttle shafts out have bushings installed and use new teflon strips on the secondary shaft plus verify your metering blocks are flat, (most are warped).

A good rebuilder can do this for you but check FIRST before you send your #'s matching carburetor away.

65 Pro Vette

I have a new aluminum intake and a new Quick fuel carburetor and under full acceleration I’m getting a whistle. I’m following this to get an idea of what it could be. No vacuum leaks externally on the intake or carburetor or any fittings.

tbarb

Do you think the engine could be sucking air from somewhere other than the air cleaner like around the air horn gasket, maybe remove the air cleaner and try it just once to try and eliminate that first.

If the carburetor is new and the engine runs well I would think the mixer is OK but you never know now-a-days.

Geralds57

Great ideas. Our water heater went south today so I haven’t had any corvette time today. Hopefully tomorrow.