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  1. #1
    Work Harder, Millions on Wellfare Depend On Us! ultramaxracing05's Avatar
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    Piston Wash on A XPL

    recently I rebuilt my engine, cleaned the carbs, and it runs a max of 5,800RPMs and a max speed of 50mph on gps.

    I looked at my piston wash and the piston is not completely black on the top.
    it only has a black circle with a diameter of about 3 inches, almost covering the piston but not quite.
    I richen the Highs by tuning them 1/4 out and ran even worse. I can hear it running worse.


    I'm running Proks and rejetted the pilot jet, to 90 per a shop in houston that runs the same, jetting. I kept my acc pump and the choke plates and everything else is stock. He told me Low speed,1/8 turn out. Highs 2 Turns out.

    I also noticed that one of my fuel pump check valves is not bad but it has a small dent. I got some replacement check valves coming.
    also how do you replace that rubber check valve holder, last time I took it off it was a pain in the ass, to put back in.

    Rave valves are not stucked, the move freely, up and down.
    I did a test with the caps off, and it ran worse, so I believe they are working


  2. #2
    SURFnTURF's Avatar
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    Quote Originally Posted by ultramaxracing05 View Post



    I'm running Proks and rejetted the pilot jet, to 90 per a shop in houston that runs the same, jetting. I kept my acc pump and the choke plates and everything else is stock. He told me Low speed,1/8 turn out. Highs 2 Turns out.
    You are a way too rich.

    Your jetting is close but the adjusting screws are way off.
    With proks I use 165 highs adjusting screw closed, 87.5 lows with adjusting screws 1.5-1.75 turns out stock N/Seat with pumps working.
    If no pumps just change low speed jet to 95 with 1.5 turns out.

    Every time you turn the mixture adjustment screw by one you are going up approx 7.5 base points on the jetting.
    I bet you are going through the juice as well with those rich settings.

  3. #3
    steach's Avatar
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    here is the jetting I used with FA

    2.0 n&s
    80 gram springs
    90 pilots
    162.5 mains
    3/4 out on highs
    1-1/4 out on lows

    Accel pump disabled.

    Get your timing advanced 2 degrees by a local dealer.



  4. #4
    Work Harder, Millions on Wellfare Depend On Us! ultramaxracing05's Avatar
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    Hey surf, I noticed my piston wash is telling me is lean. I also noticed another problem. I took my carb filters apart today to make sure my carb filters werent clogged. And they're clean. Noticed my diapraghms on my carburetor pump are pretty streched out. There are no rips on them just pretty worn out.

    I will rebuild the carbs and go from there, I went riding today and I had a good holeshot, it would rev up good to 6k and eventually lose rpm, letting me max out to 5k.

  5. #5
    SURFnTURF's Avatar
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    Quote Originally Posted by ultramaxracing05 View Post
    Hey surf, I noticed my piston wash is telling me is lean. I also noticed another problem. I took my carb filters apart today to make sure my carb filters werent clogged. And they're clean. Noticed my diapraghms on my carburetor pump are pretty streched out. There are no rips on them just pretty worn out.

    I will rebuild the carbs and go from there, I went riding today and I had a good holeshot, it would rev up good to 6k and eventually lose rpm, letting me max out to 5k.
    Look at the plugs to see if your lean.Use genuine rebuild kits as all the others seem deteriorate excessively and cause other problems.Check the check valves as well.
    Attached Files Attached Files

  6. #6
    KrunchovXPL-GTX-RX's Avatar
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    Surf speaketh the truth.

    I have heard some odd jetting but that shop told you a whopper. I suspect that those screw settings are backwards. Either the person you talked to did not know the difference and got them mixed up or it was lost in the translation, if you will.

    Now Max, as many times as it has been said on here (and most are similar to what Surf told you and would have you running a LOT better) why would you go with something so far off what we all run?

    I am just asking, not bashing.

    I will state that I prefer the performance WITH the accel pumps and stock pop (that is, 2.0 with the 95g spring). That is with a stock pipe.

    You can mess with the timing if you want but I do not per choice.

    The only other thing that comes to mind is that a water leak could cause this. Get the fuel right and go from there.

  7. #7
    Work Harder, Millions on Wellfare Depend On Us! ultramaxracing05's Avatar
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    I'm going to rebuild the carbs, anything else I do would just be like pissing in the wind, I can almost bet my problems are starting due to the streched out diagphragm on the fuel pump.
    cause it accelerates decently from idle to wot, and then it falls on its face to 5k.

    and I noticed the performance has decreased, I bet the carbs were sitting for a while and when I fired them up they worked for just a bit.

    BTW no water intrusion, I check my pistons after every ride, and I havent seen any water wash on the pistons, the sleeves are still nice and smooth with no scoring after about 40 hrs. Compression is still good.

    Surf could you please send me that info on how to check the TPS sensor?
    something about the OHMs while moving the throttle,
    Thanks for the help. everyone I'd be lost without this forum

  8. #8
    KrunchovXPL-GTX-RX's Avatar
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    That sounds like a plan.

  9. #9
    SURFnTURF's Avatar
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    Quote Originally Posted by ultramaxracing05 View Post

    Surf could you please send me that info on how to check the TPS sensor?
    something about the OHMs while moving the throttle,
    Thanks for the help. everyone I'd be lost without this forum
    Here it is :

    The 99s came with a TPS (THROTTLE POSITION SENSOR) When a TPS switch is out of calibration, the ski my run fine for awhile, then all of a sudden drop alot of rpm and run much slower, then it can pickup and run good again, then bad again.
    What is happening is the MPEM is getting the wrong signal from the TPS, sending the timing curve into a retarded mode.It may be your problem as well.??

    The test for a TPS.
    First the TPS when working properly, sends out 5 volts vdc between zero throttle and 80 % throttle, after 80% throttle, it sends zero vdc to the mpem.
    If you see 5 vdc at full throttle, you need to adjust the TPS by loosening the jamb nut on the throttle cable adjuster ( there is a TPS adjuster usually right under the glove box insert. It is inline in the throttle cable). Adjust the adjuster until you get zero volts after 80% throttle.

    To test it you need to connect the voltage meter leads to the wires coming off the TPS ( located under the oil tank on XPL's) Connect the voltmeter between the black/white and a ground. Do not unplug the TPS harness, slip the test lead in along the wire to the switch ( a paper clip works good here) . Depress the stop switch once to power up the ignition system. It will stay on for 30 seconds. Then pull the throttle lever to around 80%, the voltmeter should read zero after 80% throttle. If it does not show zero voltage after 80%, adjust it. If you cannot adjust it to get zero voltage after 80%, replace the throttle cable.

  10. #10
    Quote Originally Posted by SURFnTURF View Post
    The test for a TPS
    Should i possibly do this on my ski to iron out this as a possible cause of my bog trevor?

    Quote Originally Posted by ultramaxracing05 View Post
    BTW no water intrusion, I check my pistons after every ride
    How do you do this mate without removing the top cap and spoiling the gasket?

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