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Discussion Starter · #1 ·
Was setting my timing and adjusting air/fuel the other day. While I was reving the car, the carb all of a sudden got this high pitched whistle. It does it at around 1000rpms. When you go above that it goes away, and when you go below that it goes away. The noise started all of a sudden like I blew something out. I though it was a vaccum leak so I took carb cleaner and sprayed it around the carb, and it didnt rev or anything so I dont know if its a vaccum leak, It also doesnt seem to do it until its warmed up. Its very high pitched and annoying.
Ideas?
 

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That sounds like a vaccum leak to me. I had that same thing happen when I installed my 4V throttle body, the leak was between the TB and the intake on the back where I couldn't spray anything up inside.

I'd pull the carb and check the gasket and surfaces.
 

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Discussion Starter · #4 · (Edited)
The intake is brand new. Like I said, it did it all of a sudden not from the beginning. It was like I blew something out when I was reving it. It seems to run good but has that ultra high pitched whistle @1000rpm's. Dont think it would be the intake, I think it has to be the carb somewhere? Not sure if I should rebuild the carb, leave it alone, or what. I will investigate further to try and pin point exactly where the noise is coming from. I already tried tightening the mounting bolts and it didnt change anything. The only thing I really messed with is the mixture screws. I dont see where that would cause a vaccum whistle. I would think it would leak fuel. I am very anal when it comes to sh*t like this and it will always be on my mind. The carb is a Holley double pumper 4777 4
 

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the carb most likely has a internal leak... the gasket then acts like a reed and squeels... they can get quite loud sometimes... replace the metering block gaskets and blow thru the air bleeds when there off on the main body....tighten the bowl screws evenly and not to tight... nut driver tight... if it persists you might need to plane the main body as over time and heat cycles they pull in a u shape from the 4 bowl screws.. you can do that on a flat belt sander or with a file
 

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Discussion Starter · #7 ·
Called Holley's tech line and the guy said that it sounds like its the air squeezing between the throttle plates because if it was a vacuum leak it would whistle all the time, not just at idle. He said not to worry about it.
I dont quite agree with him because I explained that something had to have happened because it never did it before. I literally was sitting there, in the engine compartment, doing nothing and it was like you flipped a switch and the whistle started. Same RPM. One minute no noise, then a high pitched whistle. Anxious to get home from work so I can try and figure out whats going on.
 

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MY W.A.G. is the gasket between the base and the carb body..... Kinda like you whistling a tune, most of the time you dont whistle while you exhale, but get the airflow "just right" with the tongue/lips "just right" you get a whistle.
 

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If you're revving and drop the throttle closed, you get very high vacuum and may have sucked a gasket in then. Like the others have said, check your gaskets one at a time.

Mroldfart2U explained exactly what happened in my case - the gasket acts like a reed at just the right RPM and whistles.
 

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Get a length of vacuum tubing, hold it near your head (with ear plugs if it's really loud) and probe around with the other end to find where the noise is coming from. Dig there.

David
 

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Air flowing at a certain rpm is setting up a harmonic that creates an audible whistling noise. Whatever the problem is, it is probably there all the time. You just can't hear it except at certain rev's.

Did you silicone the intake ends at the block? Give it over night to cure? Made sure both surfaces were clean and free of oil or grease? If you used the cork ends was there enough gap to not squeeze the cork out?

My most likely guess would be one or the other ends of the intake at the block from the way you describe it.
 

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Discussion Starter · #12 ·
Air flowing at a certain rpm is setting up a harmonic that creates an audible whistling noise. Whatever the problem is, it is probably there all the time. You just can't hear it except at certain rev's.

Did you silicone the intake ends at the block? Give it over night to cure? Made sure both surfaces were clean and free of oil or grease? If you used the cork ends was there enough gap to not squeeze the cork out?

My most likely guess would be one or the other ends of the intake at the block from the way you describe it.
I used RightStuff and it sat for almost 2 months before I started the car. I find it hard to believe its the intake. It was not always there. I have not driven the car yet. only run it in the garage. I was standing next to the car and the noise started out of the blue. I'm gonna order a rebuild kit for the carb to get all the gaskets. If that doesn't work I will focus on the intake. One thing I didn't do yet is go back around, and tighten, the intake bolts after the engine was heated up.
 

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as a holley dealer that runs 2 or three carbs a day on our dyno i stick by my original post... i believe by the way its described its a internal carb leak... rebuild it or sometimes retightening the base plate/bowl screws evenly with stop it... you can also try loosening the four carb mounting bolts with it squeeling and tighten in a different order untill it quits... remember to tighten before you drive... and by the way... there is no vacuum to leak at the cork ends of a intake... only oil
 

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Discussion Starter · #14 ·
as a holley dealer that runs 2 or three carbs a day on our dyno i stick by my original post... i believe by the way its described its a internal carb leak... rebuild it or sometimes retightening the base plate/bowl screws evenly with stop it... you can also try loosening the four carb mounting bolts with it squeeling and tighten in a different order untill it quits... remember to tighten before you drive... and by the way... there is no vacuum to leak at the cork ends of a intake... only oil
Ordered the rebuild kit this morning, it will be here later today. Gonna pull the carb tonight and bring it to work tomorrow to rebuild during our "down time" LOL. Should have it back on by Sat. morning. I had already tried tightening the mounting bolts while it was running and there was no difference in sound. I just hope its not whistling through where the linkage goes through the base plate. I don't believe they give you a seal in the kit for that. I will let everyone know how I made out.
Thanks
Brian
 

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Your whistling sound may just be the air passing between the throttle plates and the carb body. I have a Holley 650DP that will whistle at idle because of that, as soon as I move the throttle at all, it goes away. Were you adjusting the carb when it started? You might have moved the plates, by adjusting the idle, just enough to start the whistle.
 

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Your whistling sound may just be the air passing between the throttle plates and the carb body. I have a Holley 650DP that will whistle at idle because of that, as soon as I move the throttle at all, it goes away. Were you adjusting the carb when it started? You might have moved the plates, by adjusting the idle, just enough to start the whistle.
throttle plates rarely if ever whistle... when they are closed at idle there is a strong vacuum signal to the low speed circuits(idle/transition) and when you open the throttle that signal (vacuum goes to almost zero) stops and transfers to the booster/venturi... thats why the noise stops when you open the throttle... your carb has a internal leak also........
 

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Discussion Starter · #17 ·
Rebuilt the carb and its still doing it. Im gonna let it go for now and keep my eye out for a different carb
 
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