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  1. #1
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    STX 12F no spark on one cylinder

    I can literally write a book on the two strokes but I'm just learning on the four-stroke skis. Have done plenty of ATV and car engines so it's no biggie. I'm working on an '06 12F with 114 hours that has no spark on #3 only. It fires right up and then as it warms a bit it starts idling erratically from 1k-1.2-1-1.4-800-1.5-500-2k then dies. I think it's just the ECU trying to stabilize the idle but it's getting confused being that one cylinder is not firing. It's getting fuel cause the plug is wet. You can hold throttle at 2k or higher and it revs up fine. Somebody give me some info here on what to check, voltage, coil ohms, etc. Do the plug boots unscrew? Maybe I've just got a bad boot, I just need a kick in the right direction on this. Also it has a little valve rattle. Are these adjustable or is something worn out or sludged up? All help will be appreciated and maybe a service manual link if anybody has one.


  2. #2
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    #3 has good spark now after trimming plug wire back 1/2". Boots just unscrew like the old 2 stroke ones. Also all measure out at approx 5k ohms. Injectors ohm out and all spray a good pattern. Primary (1.8k) and secondary (24k) on each coil ohm about the same. Also both coils get around 3.4v at cranking. Compression 150,150,145,145. Swapped leads to coils and still #3 doesn't sizzle water on the exhaust manifold like the others making me think something might still be up with that one. Also swapped injectors with 4 and 3 to no change. Went ahead and pulled valve cover to see what appears to be a shim/bucket system just like on the older motorcycles. I imagine with a shim kit and a bit of time I could straighten out the rattling valvetrain. Other than that all cam lobes look good and valves all appear to be moving properly. What else in the system would cause an erratic idle then stalling out?

  3. #3
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    Lake test went fine, all cylinders firing at operating at about the same temp. Still doesn't want to idle but found out it's been sitting 3+years. Probably needs a new fuel filter and a bit of injector cleaner run through.

  4. #4

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    Get the sticky thread on here that talks about almost every possible issue with the 12/15F skis. It's a great resource and goes in order of most likely to least likely....With that said, if a 12F won't idle, there is a horribly designed, expensive but easy to replace part, the dreaded idle control valve. A simple diagnosis-- Start the engine, then shut it off. If after a few seconds you don't hear a grinding/whirring kinda noise coming from the engine/intake then it's bad. If this is the case then On Rivas site it's part number 16172-3705. Also get a new gasket as well because they like to swell and the old one has always been a whore to get back in, even with dabs of grease... Good luck




  5. #5
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    You can hear the IAC motor working. I have not unhooked it to verify it's actually moving but it does make noise.

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