IROC4LIFE

Hello Everyone

Recently I have completed putting my IROC-Z back to gather with its new motor upgrade.

All was well until I swapped out my worn rubber mounts for poly peices, this is when my headache's began. With the solid poly mounts I can now feel a vibration @ 2200-2300RPM, it sounds like a oil drum rolling down the highway. But at 2500RPM is it totally gone, then at 3200RPM-redline there is a random missfire.
This is with the car sitting still in Neutral and also driving on the road.

My Ignition Specs are as follows: MSD6AL, GM HEI with new cap and rotor, Taylor 8mm plug wires, Accel Shortie PLugs Stock Heat Range for 350ci.

My timing is 18* base with 34 total all in by 2600RPM

The Techs at the local Speed Shop seem to think its the Stock Used GM coil. I tend to agree, but then we found another problem, the plugs showed a rich condion across all cylinders.

So my jetting is 68-75 on a Road Demon 625 sitting on a Edelbrock Performer RPM with GM882 heads and a Comp Cams Ex268H Camshaft, the motor is 350ci with 8:7-1 comp ratio. The altitude here is 3300ft exactly. Can anyone suggest some jets? the carb came with 70/78's and they were so rich it smoked.

Any Info or suggestions anyone can provide will be most helpful.

Thankyou in Advance

nosibear

Your engine combo sounds very similar to my first engine. Personally, I think the carb is too big for the engine, but you would probably benefit by dropping the primaries to 66, hooking the vacuum advance back up and dropping your timing down . If your total 34* of advance is coming in at 2600 and your noticing a rough run condition between 2300-2500, you may not have the advance curve exactly where it should be. Another thing you may want to check is the distributer itself, if the shaft is worn causing play, it can affect the strength of the spark.

1986redbird

theres and article on Mortec.com that deals with the high rpm miss generated by the msd boxes, it basicly says that the box must be grounded directly to the engine with the shortest wire possible. failure to do this can cause a high rpm miss in the ignition system.