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  1. #1

    Backfiring Seadoo

    Hi all

    I have just recently rebuilt a 2004 Seadoo RXP with a SC 1503 Rotax engine.
    Today I attempted to start up, on the first couple of tries she would not fire, left it for a while and tried again.
    This time the engine would crank over and backfire or misfire with a loud bang coming through the exhaust, I referred back to the troubleshooting manual, and checked the timing, the spark plugs and caps, I put new fuel in the tank and have basically have done everything the manual says, but still the engine continues to backfire or misfire with a loud bang.
    I have been working on this Jet Ski for over 4 weeks and just want to get on the water.
    Does anybody have any solutions?

  2. #2
    1-877-JET-PROS BigBoost's Avatar
    Join Date
    Nov 2009
    I would say that if you took the flywheel off then you put the reluctor wheel on wrong or your timing is wrong with your camshaft.

  3. #3
    Was the cam and crank locked when you put on the timing chain?

  4. #4
    Yes, the cam and crank were both locked in their correct position, I double checked the timing, and both 1053 timing lines were inline with the top edge of the head.
    Could maybe a bad grounding have something to do with the back firing?
    Going to try and do a compression test today, will you know what the result is.

  5. #5
    The only reason you get backfire is that the spark plug fires when the exhaust valves are open.
    I don't mean to insult with some questions, but:-
    Was the engine locked when piston 3, ( the one closest to the front of the ski) was in TDC?
    If you rebuilt the engine was the wiring harness put back correctly to each coil on the spark plug? (admitingly, this would be hard to do!)
    Was the stator wheel, put back on the flywheel correctly? There is a notch on the stator wheel that goes onto a hole on the flywheel.
    Is the cam position sensor correct?
    If you do a compression test, and the compression is vey low, then your cam timing is way off and you are getting leakage into the exhaust system.

  6. #6
    Excuse the bad wording in the last post, forgot to put the word let between will and you.
    Just finished with the compression testing on all cylinders, the results are between 135 - 140 psi, hopefully within the range.
    I do have a confession though, when I first bought this jet ski the stator cables had been cut for the use of the connectors, the previous owner had marked each wire, I simply soldered the wires together in accordance with his markings.
    Is there a possibility, that maybe if one of the wires got mix up it could cause the backfiring or misfiring?

  7. #7
    Your compression is good.
    Can you take a picture of the connector and soldering please?

    The coil in the stator has 3 yellow wires, these are for charging, and the pickup from the stator has 2 wires, blue-yellow and yellow-white, these are the CPS ( crank position sensor) to pulse the ECM for firing the spark plug coils.

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