Mod ultra engine stalling issues...

[mike_s]

Hy guys, ive got a stumper here. A '96 (ish) ultra, 850 mod with alot of extras. Its developed an interesting habit of dying at full throttle. Just like you hit the kill switch. No burbling, misfireing, backfireing or anything like that, it appears as though the ignition cuts off entirely. But heres the kicker: after the engine winds down, at about 700 RPM, the engine catches again and sits there idling as if nothing has happened. Its 100% consistent on catching and idling after this occures, but the length of time at WOT before witch it happens seems to be random, sometimes i can go an eighth mile, sometimes 5 feet. Only does it at WOT, never anything under that. The vent lines in the fuel tank are fine, not plugged, fuel pump is fine no leaking diaphragms, fuel filter is clean, no pinched lines. Im at a loss here.

Only thing that changed is the flywheel. Had a piece of steel get in there and chip a magnet, so i dug through our spare parts and found one that i believe is off of an XCR 800 engine. Triggers all line up, everything is the same except for one trigger on the original ultra flywheel. On the original there was one trigger that was about 3 times longer than the other two. Lighting coil seems to be out, but the exciter and the trigger check out ok on the stator. I dont know how having that one trigger not be longer like the stock flywheel would make any difference, but i figured id throw that out there for someone who may know.

Thanks for any input!

 

[BB454]

Ultra

What year is the CDI? I think the 97 up and possibley the 96 is a digital ignition and had a rev limiter. That different magnet could be fooling the CDI into thinking it is over reving. Usually when that happens they just miss though. To run high RPM pipes (9200) you could get the CDI reprogrmmed.

 

[mike_s]

Thats interesting, i was wondering if the CDI would be looking for a reference pulse from that extended trigger. Im only running about 8200 RPM, nothing that the CDI cant handle. It does act like its something electronic to me anyways. Hopefully i will have a new ultra flywheel and stator this weekend and change it out and see for sure.

 

[DanB]

This could be a problem with the throttle safety switches (referred to as Speed Control Assurance in the manual) assuming that you haven't disabled them by unplugging them from the harness. It's basically two switches in the throttle block. The lower switch is open at idle and the top switch is closed at idle; vice-versa when the throttle is open. If both of these switches ever close at the same time the ignition will be grounded and kill the engine. If either of these is defective it could cause the problem you describe.

 

[mike_s]

good thought, but i use an aftermarket throttle block. no stuck throttle cuttoff on my sled. only kill switches are the pro x style toggle on the bars and the key switch, which have both been disabled in diagnostics already.

besides, i can run the sled all day long without this problem as long as i dont pull full throttle. what youre describing would act a bit differently.

 

[DanB]

Okay, that's why I said "assuming your haven't disabled them".

 

[mike_s]

No worries dan, any input is appreciated.

A buddy an i are starting to think more and more that i have a defective stator. Starting to think that there is a broken wire in the exciter that is breaking contact when the coil gets hot, then as it cools back down it regains contact...in any case i will have a new mag and stator this weekend so i will replace them and post back the results for anyone else who may ever have a similer issue.

 

[mike_s]

So late update, changed out the mag and stator and all is well. I think im going to throw that other mag back in and see what happens. Knowing that i have a good stator, im wondering if that flywheel had anything to do with the issue or if it was just the stator.