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  1. #1

    Gp1200r odd behavior in pto cylinder

    Hey guys trying workout a problem i have with one of my gp1200r's , after a top end rebuild , new pistons and rings etc i have the pto cylinder down on compression( 95psi and the others are at 115psi). I took the head off and found the low cylinder looks like its never fired a shot clean as and wet with fuel. Checked the spark and its firing no problem, even swapped out the whole electric box for another and same result.
    Im thinking that its low on compression because it hasn't ignited fuel in the cylinder and hasn't seated the rings properly.
    Done a leak down test passed no worries, changed plugs and ignition same result. Got me stumped
    Anyone got any suggestions pic shows the cylinder head and cylinder. Cheers MickClick image for larger version. 

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  2. #2
    butterbean_29512's Avatar
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    Looks like that engine is running very lean. I bet if you look into the exhaust port in that pot cylinder you will see the aluminum being burned off by the high temps. Rings seat without any combustion going on.

  3. #3
    butterbean_29512's Avatar
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    Just looked at your pics again and noticed you have WSM pistons. I've used those before. They are ok as long as everything is good, but if you start running lean those pistons fail very quickly from overheating. Specifically, the ring lands will spread out on the exhaust side of the piston. Used a couple sets of them, finally moved on to ProX, been happy with it ever since. Let us know what you find when you disassemble it. Your head gasket could be leaking a little on that cylinder also.

  4. #4
    Double post

  5. #5
    Thanks for the comments...Ok put it back together with new head gasket and compression has come upto within 5psi of the others.
    No lean condition in the cylinder, piston and cylinder was as new. This motor has less than 2hrs of runtime since rebuild.
    Im just going thru the carbs again as the pto carb doesn't seem to be fueling the cylinder properly now...
    Im looking at doing the recipe with the carbs ...

  6. #6
    Hopefully you solved it by now. Probably not the case. But I take it you have the rings on the right way up ?

  7. #7
    Yep compression issue solved ...just updating the carbs atm ...can only work on it on weekends so it been a little slow...and yes rings are in the correct way...

  8. #8
    butterbean_29512's Avatar
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    If your PTO carb isn't delivering the correct fuel mixture now, it wasn't before the head was pulled, hence it was running lean. The wash develops very quickly when running it on the water, and is also burned off very easily also. I would pay particular attention when rebuilding the carbs and going with the recipe. Remember...WSM pistons are notorious for failing when run lean. I ditched my WSM pistons for that very reason after a couple of failures.

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