141bpm

Well, thats what we thought, but which part is failing under heat stress? Anyone heard of the crankshaft position sensor thing (can't remember what Yamaha calls it) going bad? Reason why I suspect it is because we already tried the ign module, the coils seem ok and both react the same. And because when it is warmed up and failed, it will spark once as soon as you let off the start button. Sort of like the coil is charged on engine crank, but never gets signal or current drop to fire spark on the secondary side until you release the start button. Based on how a coil works, the primary side is "charged" with 12V and then when the 12V is removed the magnetic field on the secondary side collapses causing the spark.

I don't think fuel loss would cause spark loss.

Hello everyone, I gave a friend an '82 XS400 that has developed an ignition problem. It started one day last summer while we were riding, it ran fine all day then backfired to a stop and wouldn't restart. Once we got a truck to get it home, it started up fine. The problem has gotten worse now to the point that we can start it, listen to it idle and rev nice and smooth then quit all in about 5min. It just cuts out like you hit the kill switch and no restart for hours. We found that the spark for both cylinders disappears and we're not sure why. We got a new ignition module from ebay to try it, same problem. We checked the coils and the resistance seems a but high on the secondary side at 17k ohms, but both are the same. Also, since this motor runs on one cylinder, we removed one, ran til it died then replaced it with the other coil and no restart. This I think may tell us that the coil isn't overheating or fatiguing since the second coil wasn't even on the bike to warm up when it first shut down. Any ideas???