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  1. #1

    rebuilding gp1200

    so i bought a 1998 gp 1200 with a lot of work done to it for $2000. when i test rode it it was perfect running on 93 octane with some octane booster cause supposedly it had to be run on 110. the next time i took it out it would turn off while on full throttle going full speed for more than 20 seconds. the spark plug in the last piston was coming loose. i took it to the shop and he tightened the spark plug and i went back to the water. now it was bogging even when i would ride slow. so the mechanic said i needed to have the carburetors rebuilt. then with the carbs rebuilt i went to the water again and the ski was still bogging a lot! so he toook apart the head and the o rings were bad and he also told me the back and middle cylinders were scratched and had low compression. now i have a friend that knows how to build engines hes actually a certified marine diesel technitian so he will help me rebuild it. my question is, what do i have to do to the cylinders to be able to put new piston rings and get my compression back? do i have to put a sleeve in them or is there something else that could be done? any help would be greatly appreciated


  2. #2

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    re-post in "Yamaha Old School Ski Discussions"

  3. #3
    Did you just call my jetski old? Lmao jk

  4. #4
    Yamaha artisan Cutlass's Avatar
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    if the scratches are bad enough, you'll have to bore and hone the cylinders bigger and install bigger pistons.

  5. #5
    Typically if the cylinders are Nikasil, you can't bore them (those may not be Nikasil). If they are, some company's will re-sleeve them though. Do a search as this was recently discussed in the 'old school' section...you'll find the links for places who do that and/or bore.

  6. #6
    yeah i just did a search. i think my first step should be to take it apart and see what size pistons i have cause maybe it already has big pistons and i have to go bigger

  7. #7
    Moderator OsideBill's Avatar
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    Moved this thread to the old school section where it belongs.

  8. #8

  9. #9
    How can i tell if they are nikasil? Mines is the non pv version 135 hp. The one that all 3 cylinders are one piece as well as the head

  10. #10
    Flying Scotsman's Avatar
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    GPr is nick plated GP is not .
    If 1 and 3 are gouged and need bored then do all 3.If you need some 1 mm over pistons I have a set of pistons 85 mm for sale.

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