High idle then dies

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gunship

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I fixed my ignition issue but now I cant get a solid idle. it dies if I set it too low but When I set it higher It goes to 1500 RPM right off of start then slowly drops until it dies. The carb is a vacuum secondary 650 cfm holley on a 318 magnum. I have tried adjusting both the idle mixture screws, idle screw, and timing in different combinations to no avail. If its a vacuum leak how do I find it? any other possibilities?
 
I've used starting fluid to spray around the base of the carb and intake manifold-to-cylinder head area. You might have blown out your carb base gasket or a hose blew off.
 
I've never really messed with holley's much, but power valve maybe? and on to check for vacuum leaks wd40, carb cleaner, starting fluid sprayed around the base, also spray it along the intake mounting bolts to the heads, a blown intake gasket will give you fits as well.
 
Sounds like an intake manifold gasket leaking. Two ways to look for it are with a length of garden hose. One end in your ear, the other move around the engine compartment til you hear hissing. Or start the car with low idle setting and open a propane tank like the kind you use for brazing. Run the propane around the intake. When the ROMs go up, you've found your leaky area.
 
Would be a good idea to determin if it's over or under fueling, then go from there.

Do you see fuel dripping inside the carb while it's running and before it dies?
When it tries to die, does choking it help to keep it running?
(Hand over the carb or whatever)

After it dies you can pull a plug and see if it's wet and smells like gas.
 
I looked and the drivers side primary is just dumping fuel at idle. what would cause that?
 
gunship said:
What would be the solutions to those?
Click to expand...

put a good fuel pressure gauge on it and see what the reading is (no more than 6.5 at any time on a holley.

pull the brass flat head screw out of the side of the float bowl (with it running or electric pump on) and see if fuel comes out, if it does then shut it off and readjust the float. if no dice pull the float bowl and check the float to see if it floats or if the needle and seat have junk in them causing them to stick.
 
gunship said:
Thank you very much!
Click to expand...

no problem

High float causes fuel to get sucked thru the booster which you seeing

Sunk or stuck float causes the same thing by not metering how full the bowl is.

High fuel pressure pushes more fuel into the bowl as the float cant shut the valve

Needle and seat can stick causing the again unmetered fuel into the bowl
 
Just on a whim I replaced the power valve and now it idles perfectly!
 
I had some backfires when dealing with my ignition issue and I happened to have a spare one laying around. I am normally a huge fan of diagnostics and not throwing parts at a problem. Thank you everyone for your help
 
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