350 HO Crate Motor

anyone having problems with the GM 350 HO crate motor? My son's has a bad off-idle stumble. we thought 2 fouled plugs, courtesy of 2 bad wires, was the cause. no luck. after removing all the plugs, 4 of them have oil on the threads, but look ok(tan) on the insulator. After replacing all 8, and 30-40 min. drive, removed again, and they all look ok. Here's some specs on our motor... New Crate Demon Carb, New HEI from GM (timing @ 10BTDC), RPM air-gap, coated Heddman Tork-step. Have run timing back & forth, checked idle mixture, accel pump, float settings. nothing we do seems to change this stumble. I'm starting to wonder about ring seal.

bought a vacuum gauge and at idle it had a constant 16" Hg and 21" at 2000rpm (manifold vacuum). checked the ported vacuum at idle and was 0" as expected, didn't move until approaching 2000rpm and was at 5" at 3000 rpm. also tried a cranking test with carb closed, pcv plugged and had 6-7" Hg.

im just not sure what this is trying to tell me. can anybody help??

Not unusual for a fresh engine to have some oil in threads. But won't hurt to check other sources for possible oil problem, like the intake manifold requiring a retorque. Sometimes it's the head gaskets that need retorque. I know gaskets say "no retorque", but I've seen them get loose, allow water into cylinders, and unseal the rings.

I don't think ring seal would cause stumble. A stumble that bad is usually accelerator pump shot being weak, occasionally low float settings. But you checked those, so about only thing I can think of is ignition problem like a weak coil, or one of those see through sight plugs causing a misreading of float level.

How does it run at WOT?

I'm not a carb person at all, but we bought the "crate demon" carb already setup for this motor, so I'm assuming the pump shot is correct. We did adjust the linkage back and forth, it moves instantly with the throtttle, but is it the correct cam, i don't know. Again its a "crate demon".

This is the 2nd HEI we've had on the car, including the coil.

At WOT it runs great!, you just have to feather it to get the rpm's up. If you just smash the throttle it will stumble so bad the motor will all but die, until you back off some, them it will pick right up. Another note, it doesn't matter what rpm you're at when you smash down on the throttle, it stumbles, bad.

thanks for the reply

here's a list of 2nd's we've tried...
New spark plugs
plug wires
New HEI
New Vacuum advance can
New timimg light
New carb
timimng from 6 to 15BTDC, still dies

WHAT AM I MISSING????

does it blow black smoke out the exhaust

did the car come with HEI originaly? if not make sure you have a full 12 volts going to the coil at all times.

it doesn't blow smoke out the exhaust, and its in an '81 camaro so yes the car had HEI originally.

ok that rules out a to rich condition find someone that can adjust the carb