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Searching for a vacuum leak
I have 2 reasons I think I may have a vacuum leak, #1- sometimes, at light throttle (cruising speed) I have a distinct whistle #2- my AFR reading on my FAST meter at idle is 19-20, cruising it ranges from 16 down to 13.
To check this I had it running and sprayed Carb cleaner around the base of the carb and the intake flange. No noticable change to idle quality. Then I put my Moroso carb cap on the Dominator, it did suck the cap down and distort it. But the carb stud held it tight enough that I don't think it could have been sucking air around the base. The motor did not shut off. I guess it could be an internal leak in the carb. So 2 questions come to mind. 1- is there another effective was to search for the source of the leak? 2- If I used 3 circuit gaskets on the metering blocks by mistake ( this is a 2 circuit carb) would that cause an internal vacuum leak. I don't think I did that but I'm 2nd guessing myself now. |
Can you replicate the whistle with the motor out of gear?
How old is the carb, does the throttle shaft rock around? |
I've only ever heard the whistle while driving. I haven't really held it at rpm while in park to see if I hear it. The carb was rebuilt about a year ago. Just a clean and new gaskets rebuild here at my shop. It's had this whistle from the begining, I just ignored it until I had reason to suspect something is wrong
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So if you completely close off the top of the carb with a big towel will it stall out?
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Does it whistle when you shut down? Like a compression leak thru the valve seats. Or only when running or both? I ve only heard that when running, using 4150s when the throttle blades have the holes drilled in them to get the transfer slots in the correct positions. One is set to low and the air is being drawn thru the holes heavily. I know thats old school tuning, but thats how we did it...lol.
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I see what your sayin about the blue cap now. Jeez you gots a serious leak. Check those metering block gaskets. Happened to me. But can t remember what it exactly was doin, it just was runnin like chit. The one hole exposed another. It may have been the air bleed channel. You ll find it, ugh, just gotta take things apart in reverse of how it went together. ✌
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From your description, it sounds like it's getting combustion air from somewhere. Not familiar with your car, but power brakes?, Some type of PCV system? These would be air leak sources.
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I have had whistles from loose fitting on brake booster.
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No idea about your engine specs but rocker cover bolts go into intake ports? Might be leaking there.
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Late last year I was coming back to the pits and noticed a whistle sound from the engine. Mine did it at idle and cruise rpms. It was more prominent on one side of the engine. In my case it was the intake gasket. It actually sucked in.
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Looks like I'm gonna pull the carb and rebuild, if it continues then I'll take the intake off to check the gaskets there. Dang..lol..
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Had an intake leak few years ago on my Firebird. Never heard a whistle but my time slips told me something was wrong. It was on the low side and wasn't obvious when trying to locate it with a spray. When we pulled the intake a sharp eye (not mine) noticed a slight stain under #3 port. New gasket solved the problem.
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Check all your plugs that may give you an idea where to look. Are your heads ported enough to where the valve cover bolts need sealant or could cause a vacuum leak?
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Scott,do you have a spare carb?Maybe swap it out first to maybe rule out the carb?Tom
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I had a buddy in college with a 383 Cuda that one Holley he had whistles on light acceleration, swapped to a different carb and no whistle.
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Use kids bubbles and blow air to find leaks around gaskets,
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