Annoying whistle (vacuum leak?)

[MrGoodpliers]

I have a 250 I6 with a monojet. It has developed a very annoying high pitched whistle that comes and goes. It is coming from somewhere near the carb. The vacuum lines appear to be okay. What do you think it is?

[DT1]

If you suspect a vacuum leak, you could connect a vacuum gauge to a manifold vacuum source and record the reading. Then disconnect and plug all of the vacuum sources from the engine and re-connect the gauge and see if your reading goes up. This will at least tell you if you have a leak in some other area like transmission modulator, power brake booster, canister or under the dash.

[k2rm]

Also check the carb to manifold gasket. I had a crack in mine that would only show up after the engine warmed up and would whistle.

[sleepertruck72]

More than likely it is a vacuum leak . I had one like that where the carb gasket was causing it. It only happened at idle. If you give it a quick throttle does it go away and come back ?

[MrGoodpliers]

Sleepertruck, yes it comes and goes at different throttle levels.

[hugger6933]

With your truck warmed up take some carb cleaner and spray around the base of the carb[with engine running] and along the intake manifold. The cleaner will be sucked into the engine at the leak and the motor will change tune and raise the RPM's alittle bit. Once you hear the engine rev up where your spraying is the leak.