I have a 383 Stroker with MSD HEI... When I'm idling, the RPM will vary from 500 RPM to 700 RPM pretty consistently, like its on a cycle. Should I be worried (b/c I already am...)?
No not worried , just inconveinant.
1 or 2 thngs
1/ The VA is not fully activated at the engine idle vaccuum...
The engine fires up on the intial advance, pulls a vaccuum , which pulls the VA, increasing the rpms... the carb is 'fixed' mixture on the idle circuit... the engine 'runs' out of fuel slows....vaccuum drops, VA goes back... and repeats
2/The counterweight springs (1 or both) are slightly light....the sperings should holsd the counter weights in till at least 200 to 300 rpms above the stable idle rpms.
If they do not.. like the VA.. they swing out after firing up, increase advance, increase rpms til the 'fixed mixture from the carb idle circuit 'runs' out... engine slows.
Note: a Non egr engine which I assume this is, runs VA on manifold vacuum with the VA being part of the idle advance (initial+VA) to give a stable idle, and easy fire up, low starter loads.