I understand how to set the base timing,, unhook tan wire,,, have 95 454 im setting and while i was setting the timing to 4 degrees,the engine wanted to stumble a lil and i reved the motor some and noticed the timing mark on balancer jump from 4 degrees btdc to 10 -13 degrees btdc,, i know motor should be a idle during timing, but the engine doesnt rev more than 300-400 rps before it jumps 6-8 degrees.. is this normal for the timing to jump that much during base timing setting, or is there other issues going on?? Distributor is from a working engine that had no problems running,,

 

Silly question but someone will ask so i'll be the guy , did you have the dizzy tightened all they way down when you reved the throttle?

 

Of course ,,the distributor was just movable enough by hand to adjust timing and everything else was in location and tight..

 

Called limp mode advance. Usually comes in at a higher RPM, such as 1400 - 1600 RPM. Maybe that year BBC GM has it coming in sooner.

RBob.