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  1. #1

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    I am about to flip out ski blew up for 3rd time

    Allright Iam about throw this thing in the garbage . Wish i could afford to do a conversion or a new ski .
    I put high compression head on then pop #1 cylinder blew .
    I found a small hole in the pulse line figured ok must be it. I put a new piston and rings in . Then went for a ride ski ran great I tuned it in , Held it wide open pop same cylinder same marks on the piston .

    Here we go again. This time I rebuilt all 3 carbs up the jets to 130 mains 115 pilots drilled the restrictors , dual feed with fuel pressure guage . I pressure tesed the motor thanks to oside for letting me use his kit . When I pressure tested it I found a bad front crank seal . So I put in new seals and resealed cases 1/2 psi drop in 10 mins . The motor goes back in and finally got to run it yesterday .
    I go out ski runs great but rich on top end I slowly start turning mixture screws in 1/8 turn at a time got the rpms up 7150 ski runs great plugs still little rich . So I go for a longer ride cruising along ski starts to slow down and bog . It shuts off but started right back up I go back to the ramp do a compression test front cylinder 120 #2and 3 145 on hot motor .

    I am so fustrated and out of money I am just trying to get the ski reliable . I have no idea what else could be wrong .

    mods to the ski are
    holeshot kit , fa's jetted 130 mains 115 pilots in line restrictor with fuel guage 2-3 psi idle 6 -7 psi ful throttlle , dual feed , reed stuffers ,pump tunnel reinforced , ride plate, island racing pump liner with a nulet 13/18.5, decked head and mild home done porting . This is a reman sbt motor .

    I dont know what else could be wrong to cause the front cylinder to blow up for the 3rd time the same way and same piston damage .


  2. #2
    SplishSplash's Avatar
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    Well, everything was fine until you put on the high comp head right?
    Well fix #1 again, put the STOCK head back on. Ride the ski easy for at leat 30 min to an hr to get #1 broke in again.
    Then ride the ski, if everyting works good, then you know your machine is working right with stock compression.
    If it blows again, the carbs are messed up.

    What octane gas are you running? Whats the piston wash look like? Plugs?
    Maybe post a pick of the pistons.
    Did you check your piston ring gap before installing?
    Saddly, so many things can cause this on a modded motor.

    Its hard to fix a modded machine when you don't know if it would even work stock.

    Good luck, don't give up, in the end you will have a good machine.

  3. #3
    philip_gpr's Avatar
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    Sorry to hear about your troubles. Clearly there is something wrong with #1.

    Can I ask what needle and seat you are using?

    If is was me I would replace the complete motor and the carbs. (enough is enough)

    Before you tear it apart you might check to see if the crank is out of phase. Put # 2 at TDC then measure the distance to the top of the piston on # 1 and # 3. They should both be the same. (thia is crude but if you can manage to get a cood measurement it works)

  4. #4
    BoostCrzy's Avatar
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    One thing I have learned the hard way is the carbed GPR does NOT like sustained cruise......there is a huge spike in ignition timing at 4700-5200 rpm......and that is also where the carbs will run their leanest..(very light throttle)..combine that with high compression and you get a very dangerous cruise...best bet is to use 93 octane gas and stay away from that 5000rpm range....especially with a high compression head....

    Heres a thread touching on the subject a bit more... http://greenhulk.net/forums/showthread.php?t=122868

  5. #5
    Dave Sharp dav_dman's Avatar
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    Quote Originally Posted by BoostCrzy View Post
    One thing I have learned the hard way is the carbed GPR does NOT like sustained cruise......there is a huge spike in ignition timing at 4700-5200 rpm......and that is also where the carbs will run their leanest..(very light throttle)..combine that with high compression and you get a very dangerous cruise...best bet is to use 93 octane gas and stay away from that 5000rpm range....especially with a high compression head....

    Heres a thread touching on the subject a bit more... http://greenhulk.net/forums/showthread.php?t=122868
    great advice, and so true. Build it again and get it right if you want...but then the flywheel will sheer the crank snout. part it out and put an rxp engine in it and ride all day. The 66v is crap and yamaha owes me a ton of money. You too. Good luck bro

  6. #6
    Moderator OsideBill's Avatar
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    Lets see some pictures of the marks on the pistons. Do you know what your bore clearances were on the piston to cylinder? if it is simply heating and doing a 4 corner seize you may have a bore clearance issue. Are you running stock sound suppression or a free flow exhaust?

  7. #7

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    Quote Originally Posted by philip_gpr View Post
    Sorry to hear about your troubles. Clearly there is something wrong with #1.

    Can I ask what needle and seat you are using?

    If is was me I would replace the complete motor and the carbs. (enough is enough)

    Before you tear it apart you might check to see if the crank is out of phase. Put # 2 at TDC then measure the distance to the top of the piston on # 1 and # 3. They should both be the same. (thia is crude but if you can manage to get a cood measurement it works)
    Iam using 1.5 needle and seats I did check pop off also . I will check crank phase what Iam thinking is maybe crank has a slight twist and cylinder 1 is so advanced its smoked the piston . Also everytime it has blown it has been when I was flat out . I will get some pics up

  8. #8

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    I have stock supression with a d plate . Its not a 4 corner seize its always right by the exhuast port and dome is chipped up . It idled fine i cant see this being a lean issue or an air leak especially with 130 main in there . this is a pic of the previous seizure i have not pulled it apart yet . is there any way the head could have caused a problem .

  9. #9

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    Quote Originally Posted by OsideBill View Post
    Lets see some pictures of the marks on the pistons. Do you know what your bore clearances were on the piston to cylinder? if it is simply heating and doing a 4 corner seize you may have a bore clearance issue. Are you running stock sound suppression or a free flow exhaust?

    With the way i have the carbs set up that is there any way it can go lean ? since i have drilled returns pressure across all 3 carbs should be the same no matter what .

  10. #10

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    Quote Originally Posted by BoostCrzy View Post
    One thing I have learned the hard way is the carbed GPR does NOT like sustained cruise......there is a huge spike in ignition timing at 4700-5200 rpm......and that is also where the carbs will run their leanest..(very light throttle)..combine that with high compression and you get a very dangerous cruise...best bet is to use 93 octane gas and stay away from that 5000rpm range....especially with a high compression head....

    Heres a thread touching on the subject a bit more... http://greenhulk.net/forums/showthread.php?t=122868


    What ever came of your ski the way your ring glands are melting over right by the exhaust is whats happening to mine . I also have a riva cut head .

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