This is with a holley 600, choke removed, no egr.

Once the motor is warmed up and idling well, about every 10 seconds or so it will start to stumble, the rpms drop, and it usually dies. If it doesnt die, it will stumble, almost die and then pick itself up.

The fuel pressure gauge stays at 6 psi and doesnt fluctuate, and my idle afr is about 12:1, as soon as the motor starts stumbling, the afr shoots up lean to about 17-18. Any ideas?

 

Sounds like your float is sticking. Or a float problem of some sort.

You'll drain it, it'll hit lean and die, then the float will drop and refill. Sometimes it refills before it stalls.

 

What Sonix said. In addition... sounds like it is loading up on fuel (too rich). Have you tried adjusting the idle mixture screws - gone through the idle tuning sequence?

Possibly a blown power-valve? I couldn't get a good idle once and it went away when I replaced the bad power valve. (Power-valve - large round, screw-in plug looking thing in the middle of the metering block. You have to take the carb apart to replace it...)

 

At idle it runs about a 11.5 -12.5 afr. I tuned it to where it reads the highest vacuum, have the idle mixture screws 3.5 turns out though. I can free rev the motor all day, but often when I let off, it idles for a second and dies. If I just start it and let it idle, its ok. The power valve is good.

 

How's it run? Like cruise is fine? WOT is absolutely stone cold perfection?

highest vacuum at idle - that's good, seems a little rich, but I can't argue highest vacuum. When it dies, it's still showing lean on the O2 sensor right before it dies?
How do the plugs look? Not loading up?

I'd still check the float level, and verify a smooth travel path.

 

umm i have my Holley 600 mixture screws all the way in (both of them) and it runs, if i pull them out anything over 1 full turn even with idle screw heaps in it almost stalls off idle. i put the screws at 3.5 turns out about an hour ago and it stalled the second i hit the peddle. try running them all the way in, i don't know if it is just my Holley but it works for me.

 

The power on cruise is weak, but a slight romp off idle is good, I have my wot afr at about 12.5. Float level is barely below the sight screws. Haven't checked the plugs, but I'll look. I have a feeling they might be a little loaded, today when I took the car out for a burn, I gave it hell and the idle was up around 1500 after, its usually around 900-1k.

 

Definately sounds like a carb issue to me, but holleys aren't my area of expertise.

I don't think your plugs are loading up, unless you're using very cold plugs, or your gap is all messed up. Check into those.

Double check linkages for binding or anything like that.

Higher idle after a high throttle run eh? assuming no binding.... Hmm, I know this should flag something for me, but i'm drawing a blank here. Have you checked for vacuum leaks? I'd do that.

 

BTW, what cam do you have in it?

 

I'd change the fuel filter to make sure it's getting the proper amount of fuel to begin with. Your problem seems to be when the motor warms up, which as we all know heat causes expansion. You could have a faulty intake manifold or carb gasket that begins to lose vacuum when the car warms up. Another possibility is an ignition control module that starts to fade when the ICM heats up. That probably isn't the case here though, since your carb goes lean before it dies. Leaking at the intake or carb could be what you're looking for, since the fuel filter doesn't seem to be a problem at idle. So, now that I've gone through all this, I'm gonna suggest you check those gaskets.

 

The cam is an Lt1, it cant be the intake gasket, but it could be the carb gasket. Ive had it on and off a lot, but the gasket always looks good and the problem doesnt change. If the gasket was leaking, I would think that the problem would disappear and reappear taking the carb on and off. I have an msd box so there isnt a module, and the timing is at about 20 base. Compression is only 7.5. I think I'm going to check my plugs. I could have a bad cylinder and the afr wouldnt show.

 

I believe I found the problem, I was having a cooling issue and my motor was running at about 250*, since I've fixed that, no more idle problems. Maybe it was detonating?

 

Check the plugs and see what they look like. Glad to hear you got her fixed.

 

Ok I didnt fix the problem, it came back. Turns out it starts to die when I turn the cooling fan on. I have an MSD ignition which is wired to the same terminal as the fan is. I'm wondering if the fan is sucking power from the ignition. My idle is at 1000 and my alternator is putting out about 15 volts. I think ill wire the ignition straight to the alternator and still havent checked the plugs.....maybe tomorrow.

 

What happened to the original wiring for the ignition that caused you to wire it into the fan circuit?