Hey guys im having trouble with this 302 i built. Soon as i get the truck running the think seems to idle at around 2800 - 2500 rpm for about 5 seconds then it will die right after that. mods include- keith black flat top pistons, isky cam .550 lift and 280 duration, edelbrock rpm performer intake, brand new holley 600cfm carb, milled heads and block, stiff *** valve springs from ISKY, and FLOWTECH shorty headers. Im thinking i have a nasty vacuum leak somewhere. Also i have to milk the throttle to keep it running when i do drive it. Any ideas?
High Idle!
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Ideally, vacuum leaks are found by passing a propane torch wand, with the gas turned on just a little, around the mating surfaces of intake manifold to heads and around the base of the carburetor. If you pass the wand by a leak, the motor will pull the propane in and the motor will rev up a little and smooth out.
A can of starting fluid (ether) with a tube attached to the nozzle will work also (like the red plastic tube that comes on a can of WD40. Heck, even WD40 will work, the propellant in it is propane. Don't breathe too much of the ether though, or you'll fall asleep
Carburetor cleaner in a spray can will also work, but again, avoid inhaling it. It is a known carcinogen.
Here's an article I wrote for the wiki that explains how to fix an internal vacuum leak if you can't find it on the outside of the motor......
http://www.crankshaftcoalition.com/wiki/Manifold/Head_vacuum_leak,_internal
A can of starting fluid (ether) with a tube attached to the nozzle will work also (like the red plastic tube that comes on a can of WD40. Heck, even WD40 will work, the propellant in it is propane. Don't breathe too much of the ether though, or you'll fall asleep
Carburetor cleaner in a spray can will also work, but again, avoid inhaling it. It is a known carcinogen.
Here's an article I wrote for the wiki that explains how to fix an internal vacuum leak if you can't find it on the outside of the motor......
http://www.crankshaftcoalition.com/wiki/Manifold/Head_vacuum_leak,_internal
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Faced with this, I'd get my tools out and remove the intake manifold to check the gaskets for "pinch" all the way around each intake port. I'd also remove the carb and check for flatness on the throttle body and at the intake manifold.Titanium said:
Are you absolutely certain that you haven't left out a screw-in plug at the manifold or back of the carb?
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Have you looked down the carb when its "idling" @ 2800 to see what the throttle plates are doing. I think you got more than a vacuum leak.
Yes i've looked down the carb while it was idling at 2800 the thing is just feeding it fuel through the secondaries. I adjusted the curb idle way low and the lowest i've gotten it to idle was around 1200 rpm and after about 30 seconds it will die. I've glanced around the intake gaskets and they appear to be set right.
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