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Old 07-21-2007
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Join Date: Dec 1969
Posts: 178
Default What's Compression PSI on '07-50HP TLR-2 Stroke

I purchased a Yamaha Service Manual for a 2007 TLR 50 HP 2 stroke.

Pretty dissappointed on contents---Vary sparse !!!

Any one know the normal compression values on this engine???
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Old 07-21-2007
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Compression should be even, no more than 10% difference between cylinders. The 50 2 stroke usually run about a 100 psi compression.
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Old 07-21-2007
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Thanks...Now I know what sort of value I'm looking for. No numbers given in manual.

I like to monitor compression season to season.

Thanks !
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Old 07-21-2007
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Join Date: Dec 1969
Posts: 178
Default Compression Checking on Yam 2-Stroke

I've been taught to take compression on a warm engine, with the plugs out and grounded.

A recent venture into Polaris 2-stroke jet skis, I learned that it is better to take compression on a STONE COLD ENGINE with the plugs IN the cylinders not being tested and the plugs grounded.

The engine will rotate faster and since cold you have a repeatable base line to establish norms.

I've tried this procedure and the above is true.

What does the Yamaha community have to suggest about this procedure ?


Also.....in jet skis "Piston Wash " is monitored. That's the areas around the outside of the piston top that is "washed" by the fuel. Viewed through the spark plug hole---it looks like small c's about the size of your fingernail, or so.

Not enough wash and the engine is running lean(hot), thus possible burning a hole in the piston.

Comments please......
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