finding vaccum leak

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Nov 21, 2002 | 08:06 PM

scott9320

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Joined: Nov 2001

Posts: 196

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From: beverly, Ohio

finding vaccum leak

got a vaccum leak on my 351 and cant seem to locate it. I can only hear the leak when its under a hard pull. checked it over with an extra fine tooth comb. just trying to get some tips on how to find this thing.

thanks in advance,
scott

Nov 22, 2002 | 05:39 AM

mic

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Joined: Aug 2001

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finding vaccum leak

Try using a propane torch, turn it on and run it near the area you
think or don't think you have a leak, if you hear your engine idle
increase you've found your leak...

Nov 22, 2002 | 09:46 PM

0u812

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Joined: Jul 2002

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finding vaccum leak

You might want to add that you don't light the torch!!! Seems obvious but to a novice mechanic it may not.

Nov 23, 2002 | 04:08 PM

Franklin2

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Joined: Jan 2001

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From: Virginia

finding vaccum leak

Do you realize you have little to no vacuum when you have the throttle near wide open? I say this because you said you only hear it during a hard pull, which says to me you have the throttle open pretty far. Vacuum is created when the throttle butterflies are closed. The more you open them, the less vacuum you have. You may still have a little vacuum if your carb is too small, but the air rushing in the engine would much rather go through the path of least resistance, which would be the carb throat, not a tiny gap in a gasket or vacuum hose somewhere.

If you can't seem to find any vacuum leaks, take the aircleaner off and see if the squealing goes away. It may be squealing around the top of the carb if the gasket is not there. Also a dirty air filter will aggravate any little air leaks in the aircleaner assembly.

Nov 23, 2002 | 06:23 PM

Ford_Six

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Joined: Oct 2002

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From: The Big, Oregon

finding vaccum leak

What you are hearing might actually be a plugged catalytic converter. Does it feel like the truck has no power? That's it then.

Jared

Nov 24, 2002 | 08:13 PM

scott9320

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Joined: Nov 2001

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From: beverly, Ohio

finding vaccum leak

o.k. I tried the propane trick with no results. tore the carb apart again, I should probably mention that I rebuilt it about two weeks ago. it's hesitating on quick acceleration. checked the power valve that came in the kit. on the bottom of the valve is stamped 7.5. is this the right power valve for this carb or did they give me the wrong kit. The carb is an autolite 2150 from a 74 351w. Thanks to all who replied and to franklin for the detailed info.