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  1. #1

    Question Black Spark Plugs. Could this be the cause?

    Hello everyone. I am new to Jet Ski's meaning I have driving them for 15 plus years but never owened one until this past year. My family gave me a 1986 Polaris SLT 780 broken. Last summer I had it professionally redone. Meaning new motor, rebuilt carbs the works. Put about 15 hours on the new motor last summer. Anyway, instead of winterizing the jet ski i choose to just start it once a week. I live in Texas so winter is pretty much a non issue. So I took the spark plugs out for the 1st time this past week and they were a black color with a little shine to them. Not drenched and not bone dry either. Now my question:

    Could the black plugs be caused by just starting it up once a week for 10 seconds and not getting the engine heated up like it does on the water to burn off the oil or do you think I have a mix problem?

    This all came to head when I changed from a stock air filter to the 3 K&N setup. Thought I should check the plugs to see where I was at. I have put new ones on and plan on lake testing this coming weekend.



  2. #2
    I transcend race Hombre! TBone14's Avatar
    Join Date
    Jan 2011
    St. Louis, MO
    Sounds lean on the low end....richen up the low speed adj.

  3. #3
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
    Join Date
    Oct 2006
    Cleveland OH
    Honestly, any plug readings on the trailer are going to be inaccurate. You cannot "tune" your engine on land.

    There's no load on the engine until it's in the water. Therefor, fuel requirements are not going to be the same.

    Run in at the lake and see what you get then.

    DO NOT make any long WOT runs until you are sure you're good. It doesn't take long to damage a piston or pistons running lean at WOT.

  4. #4
    ThrottleOut's Avatar
    Join Date
    Aug 2011
    Rochester/Corning, NY
    Like xlint said, if you're not in the water it doesn't really tell you much of anything. Changing the air intake setup may require you to adjust the high speed jets as well. How much depends on what you went from and what you went to. You should probably do a little reading on piston wash too so you can be sure you don't melt a hole in a piston and do a lean burn down.

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