141bpm Posted April 18, 2008 Share Posted April 18, 2008 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??? Link to comment Share on other sites More sharing options...
yoda Posted April 18, 2008 Share Posted April 18, 2008 I think that you have a fuelling problem. I suspect that it will be near the tank as you can run it for a few minutes so try cleaning the tank and petcock. Link to comment Share on other sites More sharing options...
141bpm Posted April 18, 2008 Author Share Posted April 18, 2008 I don't think fuel loss would cause spark loss. Link to comment Share on other sites More sharing options...
Moderator Airhead Posted April 18, 2008 Moderator Share Posted April 18, 2008 I don't think fuel loss would cause spark loss. Sounds more like a heat problem to me, when the engine gets warm something gets open circuit, not familiar with model though, any ideas Drewpy? Link to comment Share on other sites More sharing options...
141bpm Posted April 18, 2008 Author Share Posted April 18, 2008 Sounds more like a heat problem to me, when the engine gets warm something gets open circuit, not familiar with model though, any ideas Drewpy? 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. Link to comment Share on other sites More sharing options...
Moderator drewpy Posted April 21, 2008 Moderator Share Posted April 21, 2008 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. Have you checked fuses for integrity? take 'em out and bit of wire wool the fuse ends and clips. battery fully charged and charging? have you tried a completly different coil and lead to eliminate that part? there are electronic coils and contact assisted coils!! the ignition trigger is pretty robust and works on either magnetism or optical (if optical need to make sure that the cover is on as sunlight would affect running) is there 12v being supplied when the bike becomes faulty? use a multimeter probe and crank over. Link to comment Share on other sites More sharing options...
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