I have been reading threads and I can admit when I need help....
I have 2 1991 F2's. Both were running last fall. For reference Bike A and Bike B...
My ultimate goal is to keep Bike A and sell Bike B.
Bike B was running until I went to start it and it backfired one afternoon and hasn't ran since. Wanting to have one sold, I swapped the running motor from Bike A into Bike B...B motor runs in A frame, but Bike B still doesn't run.
Bike B has spark, fuel, and turns over. Compression is solid as it ran in the other frame. I have checked all of the fuses and they are still good. The choke is properly adjusted and after a short time of cranking, the will be a small pop in the exhaust but never enough to catch and run. I have rechecked the coil wiring to ensure correct firing order. I have even purchased a brand new battery.
What am I missing?

 

Have you checked that there is infact spark?

 

I have removed the spark plugs and watched the spark jump the gaps when cranking