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  1. #1

    Exclamation Ultra 250x Hesitates to acclerate (DRIVING ME NUTSSS)

    G'day everybody, my first post here, I'll try to keep it short. My Ultra 250x starts up easy but will hesitate to acclerate past 3K RPM in the water.

    Out of the water, if I pull the throttle slowly and a tiny bit, it will rev up to 7K RPM just fine with 5PSI of boost. But it I get greedy and pull the throttle in all the way quickly either from idle or when it is at partial throttle (at 7000 RPM), it will bog down and hesitate. It also blows smoke that lingers in the air. .

    My main concerns are:

    I replaced the spark plugs and they were like instantly black/fouled within 10 mins of the engine starting.

    I did a compression test and it wasn't terrible (1= 100PSI, 2=115PSI, 3=110PSI, 4=100PSI). Motor has been striped down and pistons/cylinders don't look bad either.

    I checked the timing and can't get the exhaust cam perfectly alligned, the exhaust mark is always one tooth higher than where it's supposed to be (could my timing chain be stretched?)

    I bought it at 140 hours on the clock and with a seized supercharger.


    Here's what I've done and checked so far:

    • Supercharger coating was swelling and peeling off, so I scraped it all off. The charger now spins freely and smoothly. (yes I realise I will lose some boost).

    • I've checked the supercharger belt that it was tight and wasn't slipping.

    • I opened up the I/C and cleaned it out... no oil, just some salt.

    • I checked the air trumpet/intake that it wasn't pressed against the hull

    • I replaced the spark plugs with new ones

    • I completely pybassed the supercharger and I/C by just letting the throttle body suck in atmospheric air (same result)

    • I checked and tightended all the hoses

    • I checked the oil level and ensured oil wasn't being sucked into the intake

    • I replaced the battery with a brand new one

    • The pump/jet propellor spins freely

    • I did a compression test and it wasn't terrible (1= 100PSI, 2=115PSI, 3=110PSI, 4=100PSI)

    • The engine has been dissasembled to replace the pistons (possibly bad oil rings causing it to smoke), but the pistons and cylinders all look great without any carbon buildups nor scratches.

    • Engine not hydrolocking, oil is clear and not milky.

    • There are no error/check engine codes on the dash

    • I used both the FPO key and SLO key, different readings on the dash but same hesitation result.


    PS. I'm on the edge of ordering a new timing chain and 4 new sets of pistons and rings. Idk if this will fix the problem.

    PPS. Also, when I'm flushing the engine or riding, is water supposed to come out of the hole towards the front mid right of the ski? Thanks!!!

  2. #2
    dcuhpw's Avatar
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    I’m sure more will chime in but here are a few thoughts. Compression is low but you need to fix your timing issues first and foremost. I doubt that the chain has been stretched. As for removing the supercharger coating, I doubt you will every get even close to full boost. These ogura style superchargers don’t seem to be as tolerant to anything being out of spec compared to the eatons. If you do swap pistons, go with 260x pistons or aftermarket forged. Try to get the timing marks set correctly first though and go from there. Also, make sure you have a completely charged battery before doing your compression test.

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  4. #3
    Update: New timing chain arrived and it's exactly the same length as the old chain. The new pistons came and the the ring gaps along with the piston grooves are exactly the same. I'm putting it back together and will try and get the timing perfect. At this point, I'm doomed lol

  5. #4
    make sure to set your valves this is a huge step you dont want to miss.

  6. #5
    Myself's Avatar
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    Wet plug and hesitation sounds like a TPS issue to me.


  7. #6
    Update: Thank you everyone for the replies. I'll have a look at the throttle position sensor after I put everything together.

    I have just installed the new pistons and rings and measured compression. All 4 went up by about 25% (100 to 125, 115 to 150, 150 to 175, etc).


    I poured some liquid into the head and realised some valves were leaking. They have been taken off and are currently being lapped. Their condition is terrible. They're all rough around the edges. After this I hope compression can get back to where it's supposed to be.

    I'll also do my valve clearance after I put them back.

  8. #7
    dcuhpw's Avatar
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    Quote Originally Posted by Bignudge View Post
    Update: Thank you everyone for the replies. I'll have a look at the throttle position sensor after I put everything together.

    I have just installed the new pistons and rings and measured compression. All 4 went up by about 25% (100 to 125, 115 to 150, 150 to 175, etc).


    I poured some liquid into the head and realised some valves were leaking. They have been taken off and are currently being lapped. Their condition is terrible. They're all rough around the edges. After this I hope compression can get back to where it's supposed to be.

    I'll also do my valve clearance after I put them back.
    If the head is off just do a valve job. Lapping them in will not get you back to spec. The valve seating surface needs to be within spec for valve heat transfer and good sealing. The angles and specs are all in the factory service manual. Also, as I’ve said before, removing the coating from your Ogura supercharger is a bad idea

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