hi, I've a 1983 force 85 i've changed trigger,cdi,coils and stator and i still have only spark on one cyclinder. i could see a very weak spark on the other 2 coils for the other 2 cylinders,I switched all these parts with a good spare engine and they worked fine and installed the parts from spare engine to the engine with the problem and the problem persisted. i was think on changing the fly wheel, but this part is listed as obsolete. any suggestion please?

Have you eliminated the stop circuit (black/yellow wires)?

if you're talking about the two grounding cables from the cdi's, yes they're eliminated.

I don't remember what color the "stop" circuit wires are on this motor.
But I am speaking of the wire that grounds when the ignition key is turned off.
Merc series Forces used a black/yellow wire. I THINK it might be a white wire on yours.
Check behind the keyswitch.
The Force OBs died where I live in the mid 90s. I haven't looked atone since then.

could be possible to have a bad flywheel? i have spark only in one cilynder

Not likely