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  1. #1

    No compression in middle cylinder

    I have a 2002 yamaha suv with around 100hours on it. I recently installed a primer bulb on the fuel supply line to help pressurize the tank and prime the carbs. It worked great for about 1 hour. The ski died while going full throttle at 49mph on gps, then it would not accelerate pass 5k and die, then 4k and die. I suspect the primer bulb so I removed the primer bulb and it rev'ed up fine. But it sounded strange so I pulled spark plug off and put back while engine running and the 2nd cylinder makes no difference in sound. Long story short, the 2nd cylinder has zero compression the other were 115psi each. Could the primer bulb restrict the fuel float and cause this? Any insight on this is much appreciated!

  2. #2
    Myself's Avatar
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    Look for a loose oil line or creased fuel pump check valves on center cylinder.

  3. #3

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    Just spitballing, but...

    Maybe the primer line was leaking fuel into the middle carb. That changed the fuel/oil mix in the middle cylinder and caused piston/ring/cylinder damage.


  4. #4
    Hi guys, I was able to take it today. The cylinder wall is scorned. The piston ring maybe gone. Can it still be fixed? What can i do with the middle cylinder wall. Please advise. Thanks.

    here are the pics. I thought the piston was done, but it didn't look that bad. I was suprised it showed 0 compression.
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  5. #5
    Can the sleeve be machined or re-sleeved or honed out. I saw a junk is melted on the cylinder wall.

  6. #6
    Any idea on how this could happen?

  7. #7

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    The metal on the cylinder wall is probably aluminum that melted off of the piston and adhered to the cylinder. You should be able to sand or hone it off. Only issue is that you could hone too much, causing the cylinder to go out of spec and have low compression. Then you'd have to overbore or re-sleeve the cylinder.

    You'll probably have to replace the piston and rings.

    Make sure you figure out what caused the failure before putting the motor back together. That sort of damage was probably caused by an oil injection problem.

  8. #8
    butterbean_29512's Avatar
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    When you say primer bulb on the fuel supply line to pressurize the tank....what type of bulb did you install? A bulb used on a boat, or a plunger type used on a ski? If it ran bad enough to have to install a primer...I hate to say it...but attention should have been shown long before now. Now that that is out of the way....yes its fixable. Is it worth it? Depends on what else is broke. Crank, cases, sleeve? If the crank and case is good, bore to the next oversize and reassemble.

  9. #9
    Myself's Avatar
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    All 3 are lean, center especially lean. Pull the carbs and check that center one for creased fuel pump check valves. It's a well known and documented issue on the 65u 1200. It needs the balanced return mod and slight jetting change. VERY reliable after that.

  10. #10
    I use the boat style primer bulb. installed in the fuel supply line.

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