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  1. #1

    80PSI compression, Please Help

    Hi, am new to this forum. So would like to say Hi and say this is a very helpful site.
    i have a 2000 GP1200R with about 41-42 hours, don't really have time for it. But decided to do something with it. It's been sitting for about a year or two. Pulled out the carbs and had the carbs rebuild for the second time, last time they got rebuild was about 4-5 years ago. When they first rebuild the carbs, the place that did it for me eliminated the oil pump and replaced the reeds. So this time around I removed the carbs and had a local jet ski service shop rebuild the carbs. Found the motor FULL of oil. So while the carbs were out getting rebuild, I went ahead and removed all the oil in the motor and drained gas tank and added some fresh fuel/oil, installed wave-eater clips, flame arresters, reed stuffers and free flow. It already had D plate and chip Long time ago.

    After I got the carbs back from being serviced, I installed everything back. And started up just fine. First crank actually. Took it to the lake to try it out. Ran pretty descent, from what I can remember. But a lot slower than I remembered. Today I pulled the plugs, and also did a Cold Motor compression test, and it gave me about 80 psi across all three cyclinders. I need some help. Also while at the lake, this ski was SMOKING more than I remembered it did long ago. I think or shot for a 40:1 ratio synthetic 2 stroke oil with 93 octane fuel.

    i've included some pics of the plugs after about an hour or two of testing at lake.
    Sorry for the Long post







  2. #2
    Myself's Avatar
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    80psi is very low but it's even across all cylinders so I'm guessing your gauge is not accurate. Take an ohm meter to those plugs, looks like the one far left in pics might have taken a dump leaving you to run on 2 cylinders.

  3. #3
    I have read several threads on this forum where people have stated that the compression readings on these machines should be at least 110 psi. With a 5.9:1 compression at sea level the stock compression should be 86.73 psi. What am I missing?

  4. #4
    Almost's Avatar
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    What kind of gauge you using? If it's a harbor fright guy it won't work, the hoses swell and don't get a good reading and don't read higher then 80-85psi. A new gp1200r should have compression of 120-125 psi. Anything lower then 100-105psi is due for a rebuild. Compression should also be even or within 5 psi of each other as well.

    Also, that oil in the crank case is perfectly normal. When the fuel/oil is sprayed into the crankcase a majority of the oil falls out of the gas and pools in the bottom of the crank case. The crank webs splash the oil puddle and help lubricate the bottom end. That's why you have those 2 oil passages on each side of the crank web on the upper side of the crank case. The oil gets splashed up and falls in those holes to lubricate the main crank bearings.

  5. #5

    GP 1220R compression

    Quote Originally Posted by Almost View Post
    What kind of gauge you using? If it's a harbor fright guy it won't work, the hoses swell and don't get a good reading and don't read higher then 80-85psi. A new gp1200r should have compression of 120-125 psi. Anything lower then 100-105psi is due for a rebuild. Compression should also be even or within 5 psi of each other as well.

    Also, that oil in the crank case is perfectly normal. When the fuel/oil is sprayed into the crankcase a majority of the oil falls out of the gas and pools in the bottom of the crank case. The crank webs splash the oil puddle and help lubricate the bottom end. That's why you have those 2 oil passages on each side of the crank web on the upper side of the crank case. The oil gets splashed up and falls in those holes to lubricate the main crank bearings.
    I too am new to wave runner repair and this forum. According to my Yamaha Service Manual the compression spec on this machine is 5.9:1 which equals 86.73 psi at sea level. Where is everyone coming up with these 110+ psi numbers? Like I said I am new to all of this and trying to figure out what I'm missing. Thanks to anyone who can shed some light on this subject.

  6. #6
    04gtxsc's Avatar
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    correct should be in the 120 range for a stock motor.
    Your gauges are probably reading wrong. best i remember they wont even run if its 80

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