Hello Gents,

The Iroc is stored away, this tech question is regarding my '79 Corvette of 24 years, a kind of "winter beater" these days.

I put a 400 sbc w/vortec heads with a 212/218, .487"/.495" hyd roller years ago.

For various reasons, I recently checked the exh gas temps at the header primaries.

At idle, with my 13.2 sec Quadrajet & performer, all the primary tubing temps adjacent to the heads were in the 475` range, except for cylinders #8 & #2.

The engine seems to have a trembling idle different than I remember, with 19" of vac in neutral.

Didn't do a compression check, but the plugs seem clean.

Pulling the #8 plug wire doesn't seem to drop the idling RPM much at all though.

All the rockers seem to be moving at idle as well.
Maybe burned valves?

Thanks for any ideas.

 

You can use an inductive timing light to make sure the plugs are all firing. Clamp the pickup onto each plug wire. When that plug fires, the light will flash.

 

Thanks for your reply. Good point. Ill try that. Might be time for an all new 400sbc after 12 years anyway.

 

Yup.. Cyls 2 & 8 are definitely firing. Lit up the timing light just fine.

 

So you know it's not an ignition/plug problem. It's unlikely a fuel problem to individual cylinders with a carb. That leaves a mechanical issue.

Was it running fine when it was last driven? Are the plug wires on correctly (Proper firing order)?

 

Well as far as being a running fine engine, I would say it's been a mild incremental degradation in idle quality. Nothing all of a sudden.

The plug wires are routed correctly, but there is an occasional uneven pop-poping at idle, (unrelated to the cam duration).