slight misfire & crazy tach, but perfect w/spout plug out

[S351 R]

slight misfire & crazy tach, now think its a FAST problem

New clues trying to trouble shoot a slight misfire and a stock tach that dances around above 1500 rpms. Even a new TFI module changed nothing.

If I take the spout plug out, very smooth engine and tach.

Is this a FAST problem, or which part of the ignition might be to blame.
Thanks again for all the help.

 

[S351 R]

Yeah I know this is one of those shot in the dark posts...

However, perhaps since this is only effected when spout is in and thereby using ECU control and spark advance, could there be a configuration or ECU problem?

Timing is at 36 degrees for all surrounding cells and distributor has been synch'd with FAST
All else is pretty darn good considering the early stages of tuning.