Banshee problem, anyone have a clue?

[kc 300EX]

Ok, my friend has a banshee and has a major problem, he can only get it to run off one cylinder? I dont know much about the problem but just taking a shot in case someone has an idea. Brand new pistons and rings, new domes on the cool heads, spark plugs are fine, stock compression both cylinders, everything has been taken apart and put back together perfect, he has no idea, sooo, anyone?

[trx400ex]

are both plugs firing?
is he getting fuel in that cylinder?, check the carbs and the reeds

[James70214]

Check both spark plug wires.

[kc 300EX]

he says both plugs have spark, reeds and carbs are fine

[barbwire44]

There is a little black box under the gas tank you can find it by tracing the wires on the clutch cable to it. Disconnect the wires and see what happens. Yamaha has had a lot of trouble with this component it works as a safety and when it goes bad the bike will only fire on one cylinder.

[MadcapEX]

Mine would drop a cylinder after I rode through water,after it had time to dry out it would be fine. It also dropped a cylinder when I first got it because the carbs were way out of sync.The throttle cables were screwed up and one slide opened way before the other,so it would run on one cylinder up to quarter throttle then the other would fire,it was weird. Man once I got it right though.BLING BLING