Is my Holley off key?

C

clutchdust

Millionaire Playboy
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Lately I've noticed my Holley has been whistling at me, and every one else within about 100 yards. I have this nasty vacuum leak that is just screaming loud, even with the hood down. I used some spray carb cleaner to identify where it's coming from and it's right at the front, in the general area of the vacuum take-off I use for my distributor. I pulled and capped the hose to make sure it's not actually the hose itself, but the whistle is still there. I pulled the carb off and the gasket looks fine, absolutely no indications of it being blown out or damaged.
Not only that, but I have removed the throttle plate from the main body of the carb twice now, the first time to check condition of the gasket and the last time to check for obvious signs of cracks/failure/damage. I filed down a couple of casting imperfections but nothing I've done so far has made the problem go away.
I rebuilt the carb about two years ago with fresh gaskets and a Holley master kit so nothing is really that old.
Has anyone else seen a vacuum failure in this area? Any other ideas? I suppose it could actually be from the vacuum port, if that's the case how do I fix?
 
Hold a hose to your ear and try to locate the source of the vac leak that way.
 
O.k. The damn thing won't stop whistling. It's driving me crazy! I know it's a goddamn vacuum leak too! I did the hose trick and all I can tell is it's coming from the front of the carb somewhere around the throttle plate. I don't know if it's the plate to the body or plate to manifold that's leaking. I replaced the TB to plate gasket and made a new base gasket. I also thought it might be the vacuum take-off up front so I used some JB Weld to seal that up. Finally, just as a testing tool I smeared blue silicone all along the top of the throttle plate to see if maybe it's cracked. Just as every time before, as soon as I put it all back together it sounds fine. I go drive it 2 or 3 miles and everything still sounds good. I park it overnight and when I start it in the morning the thing whistles like an ex-con in a cat house.
 
Try getting some carb cleaner (with the little straw looking thing so the spray is directed in a small area) and with the engine running, spray it where you think the leak might be. If the engine picks up speed, you found where the vacuum leak is. It may be in the throttle plate itself, on the sides where the butterfly rods come through the plate.
 
Already done that.
I think I may have finally figured out where the leak was coming from. After taking the throttle plate off several times to check/replace gaskets and stuff, I ran it again today. This time the leak was quieter, but still there. I believe it was actually coming from the plug in the bottom of the metering block. I believe this, but don't know what that plug seals, air or gas. Anyone want to comment? I smeared some silicone over the plug for now to see if the leak went away, and I don't hear it anymore. I'll probably take it off this weekend and seal it permanently with JB Weld.
 
GM had continuous problems with squeeling Holley carbs, and I've seen several, too.

The squeel comes from the carb throttle plate (base plate), and is caused by a slight leak between the throttle plate and the throttle plate gasket in an area exposed to manifold vacuum: The carbs with the problem are always the carbs that only have 6 throttle plate screws: Holley did not use all 8 screws or even tap the holes for the center 2 screws (between pri and sec) on many carbs. The air leaks through one of the base screw holes without a screw to the channel that goes from the primary to secondary idle transfer channel. Normally, the carb will not whistle when cold, but the noise develops as the engine heats up.

It was probably a cost savings issue by Holley or GM to not use all 8 screws in the baseplate (Mopar used a roll pin the size of the screw in the carbs of the same era). You can solve the squeel problem by tapping the holes and installing the 2 screws.
 
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