About 2 nights ago i drove my truck pretty hard and long. the truck drives fine but but a middle way through the night a strange whistle was coming from the engine. What could this be (vacumm leak?) There is some gas (and has always been on the left back part of the carb. Whats happening and can i fix it. Thanks

 

Take a can of carb cleaner Chris and spray around the carb until you hear the vacuum leak & whistle stop.
That will be where your leak is.

Check the butterfly shaft of the carb,as they leak when they are wor out.


[i][font color=blue]Dennis[/font][i]

[font color=red]Calgary,Alberta,Canada[/font]
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Mine does(did) the same thing until I switched carbs. I did the spray test with no luck. When I put my hand over the top of the carb it would quit. Didn't seem to make a bit of difference in performance.

In fact, one old timer I talked to said that a well-tuned carb will whistle a little-didn't believe him cause mine wasn't well tuned.

J, Boggs

 

My 390 does the same thing, but I can't do the spray cleaner thing, because it only whistles when I give quite a bit of throttle while under load. I can't get it to whistle at all when parked. My whistle is extremely quiet and high pitched, almost like a muffled scream. I've been told that it's a very small leak at my intake gasket, but haven't had enough reason to address it.

Greg
67 F100 CCS 390 FMX

 

yea same with me i cant here it at part either. i want to get a rebuild kit but I dont know what type of carb i have.

 

 

Often times this sound is indeed a leak. But I'm not sure how many folks know that it can also be caused by worn throttle bushings that operate the butterfly valves (the ones in the bottem of the carb). You usually see this with pretty old carbs, but I've seen it with carbs only ten years old. When worn, they can generate a constant high pitch whistle, which can also change as you modulate the throttle. There are rebuild kits to fix this problem if thats what it is. Hope this helped.