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  1. #1

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    XLT1200 compression 120/120/100

    I may have found the issue with my xlt1200. The compression is down 20psi on the number 3 cylinder. These are new cylinders, pistons and rings from SBT, and the ski is now premix, with all of Oside Bill's updates done. The question I now have is, can I get away with just new rings to boost the compression to where it should be, or is this now a crank issue? When I tore it down, the crank looked and felt perfect - very smooth with absolutely no play and all bearings felt great. Any ideas why one cylinder would be less than the others? I'm slowly slipping into madness with this thing.


  2. #2
    TX21's Avatar
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    Motor history? Fresh rebuild with no run time? Lots of directions to go here, Johnny number 5 need input

  3. #3

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    I put the new top end in last season. Right from the start, I felt it was smoking too much, but the compression was good, so I figured it was a result of going premix. Now, I don't think so. I followed Oside Bills recommendations to the letter for the mods, so I'm wondering why the thing isn't running right. It's got lots of power out of the hole, great top end, but the idle is very smokey. Start up creates a huge cloud of smoke. Exhaust gasket maybe? Any ideas greatly appreciated.

  4. #4
    Yamaha artisan Cutlass's Avatar
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    What kind of oil are you using? Some oils smoke more then others. But beware, smoke is normal. Post a video of the smoke show and we'll let you know if its ok

  5. #5

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    Here's a video of my smokey xl1200


  6. #6
    TX21's Avatar
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    She does smoke a lot. I don't think its a gasket thing. My gut says mix is off or the carbs are dumping too much fuel in there. That is a big guess though and it dosen't make sense why it lost compression. I would think if you have to much oil or fuel it would only run crappy not drop compression.

  7. #7

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    Thanks for your input. I'm going to turn the low speed jets in 1/4 turn and see what effect that has. On the xlt1200, it's a real pain because you have to remove the exhaust to get at your t-handles. A buddy suggested the exhaust gasket could be leaking, but I agree with you, it doesn't seem likely. I did a very careful job reassembling the motor and doubt I missed a simple thing like a gasket improperly installed. I'll post my results.

  8. #8
    TX21's Avatar
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    Quote Originally Posted by snowman12 View Post
    Thanks for your input. I'm going to turn the low speed jets in 1/4 turn and see what effect that has. On the xlt1200, it's a real pain because you have to remove the exhaust to get at your t-handles. A buddy suggested the exhaust gasket could be leaking, but I agree with you, it doesn't seem likely. I did a very careful job reassembling the motor and doubt I missed a simple thing like a gasket improperly installed. I'll post my results.
    What do the plugs look like?

  9. #9
    you dont just loose 20 psi compression without something going on....you could have a ring sticking.....did you measure the ring end gap on each ring before installing them on the pistons, or measure the piston to cylinder wall clearance before installing the pistons?

  10. #10
    silvercrxsir's Avatar
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    I had an issue with an sbt top end that had too much piston clearance,was measured at .0085 when it it should have been .005 needless to say the pistons were banging up the cylinders,but sbt ended up replacing it.you should start by checking your plugs and tell us what they look like and possibly pull off the head tosee if the cylinder walls are scored

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