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crprestridge

Yamaha YFZ450 compression?

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11.9:1

I dont think he is asking about the compression ratio... Stock compression should be 120psi plus... Im pretty sure you have to disable the auto decompression on it to get a good reading or you could do a leak down test on it...

Edited by jigolbeep

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I dont think he is asking about the compression ratio... Stock compression should be 120psi plus... Im pretty sure you have to disable the auto decompression on it to get a good reading or you could do a leak down test on it...

Yes, I believe stock is:

Compression Ratio 9.2x1

Compression 834 kPa (121 psi)

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had my compression checked and was about 170 lbs. you think i should run higher than 91octane?

170 is pretty high, what kind of mods do you have? If it is really 170, then you should probably atleast run a mix of race and pump gas.

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only mods i had when my local atv shop checked my compression what yosh pipe, moose racing jet kit, k and n filter. the guys that checked for me have been doing it a long time so i trust them. we just finished re-jetting and took air box lid off, exhast cam mod, removed spark arrester, and am waiting on rev box and 15 tooth front sprocket. we checked the compression because we couldn't get the jetting right and thought maybe a valve had messed up. have since gotten the jetting right though.

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