1991 force 4cyl 120, misfiring on 1 and 2

[Jasper8301]

Hey guys. I need help with this engine. We had to install a Thunderbolt ignition system from another used engine to this one. It starts easy, but only seems to fire on 3 & 4 until we rev the engine wide open. Then it fires on all 4, but has a miss. We checked with a timing light and it fires on 1&2 only nearly wide open. The timing is set right according to the light. It has old gas and we added staybil and are trying to run that out as it is very difficult to siphon. We replaced the switchbox on the engine with no help. The trigger checks out good. Spark plugs are new. coils seem to be ok since it will fire at high rpm. I guess my question is, why does this engine only run on 3&4 at low rpm and all 4 at high rpm? and any info on why its missing would be greatly appreciated,,,,Thanks

 

[thompy]

Re: 1991 force 4cyl 120, misfiring on 1 and 2

have you cleaned the carbs

 

[Jasper8301]

Re: 1991 force 4cyl 120, misfiring on 1 and 2

Finaly found the problem (trigger), but I went the expensive route and replaced everything and also found out to NEVER try and check for sparks without all your plugs grounded and grounded well. I made a plate with 4 threaded 14mmx1.25 holes and mounted all 4 plugs in it and bolted to my engine ,,, excellent fail safe idea if I may say so,,,good luck ,,,hope this helped someone