I recently restored my engine (327-250hp), also intalled a Petronix coil and ingnition system. Engine ran fine for several months, however now she immediatly stalls out when I release gas pedal. Engine starts fine but will only keep running when I stay on the gas pedal. Any ideas?

 

Adjust the idle speed screw (on the driver's side carburetor throttle lever).

 

Check the idle speed adjustment screw on the left hand side of the carb and make sure it is making contact with the base so it will hold the primary butterflys open slightly.

Also check your fast idle linkage on the right side of the carb. You may have been getting your idle speed off a stuck fast idle cam and it has now moved.

What is your minimum idle speed with your foot on the gas? It should idle easily at 450-500 rpm.

 

Of course I checked the idle screw and had to crank it up to get the idle to 1800 rpm just so she won't stall out immediatly while I take my foot of the gas pedal. The engine idled well at 500 rpm, then all of the sudden she stared stalling out. Its not the idle screw!

 

If the engine runs fine at higher rpm without missing, sputtering, or backfiring then i would check the fuel system.

 

Since you restored the engine(rebuilt) you might want to retorque the intake manifold bolts. You might have a vacuum leak.

 

How about in no particular order:

Water in the gas.

Idle circuit in the carb is plugged.

Your Pertronix is dead. Put a test light on the distributor side of your coil. It should flash on/off (not bright/dim) while the engine is running. Slow the engine to the speed where it wants to die and see if your light is still flashing as the engine dies out. If it doesn't flash, you have a problem inside your distributor that is not allowing your distributor to break.

 

The Pertronix, being a solid state module, will normally be good or bad. Either the engine runs or it dosen't. The Pertonix needs full voltage to operate properly. If the battery is low on charge, the voltage could be under what it takes for the Pertronix to work. When the engine is being run at the higher speed, the alternator is supplying enough voltage for the Pertronix but when you let off the gas, the engine speeds drops, along with the voltage causing the Pertronix to stop functioning. Make sure your battery is good, put a full charge on your battery, and then see what happens.

 

Also check your PCV valve. Stuck valves can create a vacuum leak.

 

Well, I don't own one of these things and don't intend to. I also know nothing about this particular item. You may have hit on something if the owner has a bad battery. Just out of my own curiosity, and anyone else interested, what voltage does it take to make one of these things fire?

It'd sure be nice if people that raise issues would reply back with the solution after getting the advice offered.

 

Lets start with basics needed for an engine to run, air/fuel/ignition/compression/timing.
Compression
Low compression typically results in blow by and low power. Not typical of a recent rebuild and not the symptoms you are reporting.
Ignition
There are a number of good methods to test the ignition system. For simple quick go/no-go testing I use an old inductive timing light. I test every cylinder for consistent pulses from the light. For finer tuning, I have a Sun engine analyzer.
Timing
This probably is not your particular issue, but worth checking while you have the light out checking the ignition. Check the operation of the mechanical and vacuum advances. If the avance is stuck full on, could cause your problem.
Air/Fuel
Most likely the issue in you case, but is it too much air or too little fuel? Vacuum leaks will lean out the mixture, plugged passages in the carburetor will also lean it out. Rich will be visible due to black smoke at the tailpipes. Vacuum leaks can be found by spraying carb cleaner around the intake and carb body and vacuum lines. The rpm will change if spraying carb cleaner near a leak. Another rare issue is reduced intake vacuum due to flattened cam lobes or skipped timing gears. In your case, assuming it runs OK off idle and has power at high rpm, I doubt these are the issue. Reduced vacuum will result in requiring the throttle being further open in order to get enough fuel to run. When installing radical cams, which result in lower intake vacuum, we would drill holes in the throttle plates to let air through and close the plates so the idle passages and transition slots would again function. Since your engine ran well after the rebuild, I doubt it is low intake vacuum due to the cam profile, since this would have appeared when you first started it. Plugged passages in the carburetor for the idle passages and transition slots will cause a lean mixture. A blown power valve will cause a rich mixture. A test to verify which you have is to look at the plugs after stalling. Sooty-rich, white-lean (and hot).
This is by no means an inclusive list, but some generalizations to narrow down where your problem is.

 

Sounds like choke?

Lived in St. Pete (on the key) 10 years USF Alumni... Andy

 

karista has left the building!