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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

    Join Date
    Nov 2009
    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
    Join Date
    Oct 2010
    Madison, WI, USA
    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''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
    Join Date
    Mar 2006
    United States
    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
    Join Date
    May 2006
    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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