High-speed misfire, 2008 SM

Hey guys, hoping someone out there can give me a hand. Got a problem with my 2008 400 SM. It did 18000 trouble free miles but then for the last 800 miles or so it's developed a problem. At 5000 rpm it starts to misfire, and by the time it's at 7000 rpm it won't rev any further.

Bike is running 3x3 plus JD jet kit and a full exhaust system and ran flawlessly with that set up for 15000 miles across central Asia to Mongolia.

Misfire doesn't happen when engine is cold, only when the engine is getting towards or at normal operating temperature.

So far I have checked:

  • Ignition Stator coil resistances: my first guess given the symptoms, and got the following:
    Signal coil reads 0.3 Ohms, Clymer says 0.05 to 0.2 Ohms, not sure I believe my multimeter to be accurate at such low resistance, but this could be the cause except I thought the usual failure was low resistance?
    Pickup coil reads 450-620 Ohms depending on engine temperature, Clymer says 390-600 Ohms, and mine is at 450 Ohms when colder, which I assume is when it should be measured
  • Carb cleanliness - had the floatbowl off this morning and it's spotless in there (well it was until I took it apart in a dusty Ulaanbaatar car park...) :thumbsup:
  • Spark plug - it had a 10000 mile old iridium one, in there, swapped that for a brand new standard plug and it's exactly the same
  • Carb breather tube - not trapped or blocked or otherwise messed about

Am I right in thinking that the resistance specifications for the ignition stator coils are cold specs?

If I was in the UK right now, I'd swap my stator for one out of a mate's bike and see if it cured it. Out here, that experiment would cost me a fortune in shipping costs (£200 or so for a stator and probably the same again to DHL) so if I can't find a stator assembly somewhere in Russia I want to be sure before I commit to the cost...

That sounds liike a statorf ail . They test fine but the first sign is a high speed miss that gets worse over time. It can also be a failing ignition coil. But I bet it is one or the other.

Balls. I was really hoping I was wrong! :ride:

Thanks for the reply. Guess I'm looking for a new stator in Russia then, apparently their customs guys are still massively delaying shipments in from other countries... :thumbsup:

oil fuel contaminated?

Thanks Eddie - hadn't thought of that. No, I don't think so, as there's no smell of gas at the oil filler (everything cold). Early in the trip I had the engine hydro-lock after leaving my Safari tank fuel tap on overnight a couple of times (and did not have this problem those days), but have got into the habit of turning it off whenever the bike's stopped, and not left it on since eastern Iran, and that was a month, three oil changes and 8500 miles ago!

Also, if it was gas in oil, I'd expect it to disappear by the end of a 300 mile day, with the oil at 75-80degC for most of that time - or would it hang around even after that?

For anyone stumbling across this thread trying to diagnose a similar problem - yes, this was the stator.

No new stators available in Russia, and not happy to use a bodge repair for the BAM road, could get stranded somewhere awkward. So hung around in Ulaanbaatar for a few days waiting for one to arrive there (quicker than waiting for it to clear Russian customs had I carried on with the misfire to Irkutsk or somewhere).

New pattern part from Electrex World in the UK was 1/3 of Suzuki GB price, including delivery to Mongolia... :)

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