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  1. #1
    Bajacali's Avatar
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    Engine help needed.

    I recently rebuilt my 08 px due to a saltwater injection from a bad intercooler. After finishing the job I now have a boat that won't start I have plenty of experience with automotive, but this is my first Rotax. What is happening is that it cranks but won't start after cranking for 15 or so seconds, it pops out of the exhaust. Everything went together well which should have been my first indication all is not going to be that easy. I did lock that crank and cam with the #3 TDC. If this is a timing issue like I believe it to be, how can I correct it? What is it that I've overlooked?


  2. #2
    RXP rider's Avatar
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    Most likely you have a bad timing since it backfire. I would take a look at the timing again.

    ---------- Post added at 08:18 PM ---------- Previous post was at 08:16 PM ----------

    I assume you already have chect the ignition, injectors spray correct ect

  3. #3
    Bajacali's Avatar
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    The timing is perfect. The injectors are spraying and I need to look at the spark closer.

  4. #4
    Moderator beerdart's Avatar
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    Did you reuse the crank? What was replaced?

  5. #5
    suck my wake's Avatar
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    It's timing, double check your lockdown points with the crank and cam. Do the crank first then check the cam, make sure the crank lock tool is in the hole and not past the crank weight. Also check and make sure the pin is still in the end of the crank and the trigger wheel is in the proper position, the flywheel and trigger wheel should only go on one way.

  6. #6
    speedskixp's Avatar
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    Quote Originally Posted by beerdart View Post
    Did you reuse the crank? What was replaced?
    Same crank but never hydrolocked to cause the crank gear to slip. I talked to him today and a few tmes along the way in his build and though I am not there in person to see he has confirmed that #3 is tdc, crank/cam locked 1503 marks line up near perfect. All injectors are spraying but spark is very weak on cylinder 1 and 3 and #2 seams to spark a bit stronger. It pops through the exhaust after cranking for a few seconds and not starting, Almost as if the fuel is building up and finaly ignites. Last I talked to him he was going to confirm that the crank sensor and engine temp sensor wires are not crossed.
    My first thought was also a timing issue but after talking to him more and him explaining how the timing is set I dont see how that could be wrong unless the encoder wheel is on wrong wich I cant see or the crank gear slipped and I doubt that also but who knows.. Also dont think timing would cause a weak spark. Maybe a bad connection causing intermittent spark and causing the sudden backfire after fuel builds up. Any and all input welcomed.

  7. #7

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    do a compression check. that'll at least tell you for sure that the timing chain is on correctly. make sure you have a fully charged battery.

  8. #8
    Gone in 3.0 seconds... RXPT400's Avatar
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    If your time was set right check your crankshaft position sensor installation and connection, see if the right plug is in the crankshaft sensor, also check your camshaft position sensor installation and connection those are the only 2 sensors that tell the ECU how is timing and beside the ECU also they will give you weak spark...

  9. #9
    Having Fun jp1300r's Avatar
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    Getting any codes? I think its possible to cross the knock sensor connection with the crank angle sensor connection.

  10. #10
    mine did exactly the same, but mine turned out to be water in the fuel tank, over 1 gallon

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