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yz high end sputter/ compression test question

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hey guys picked up a 2005 yz85 for my son the other day. The bike will start and run/idle fine but i would say around 3/4 throttle has a bad sputter. Any idea what the compression range should be? when i do the test should i warm the bike up first?

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Sounds like the main jet is too small or too big. It's hard to say without looking at the plug.

Go to the yamaha 2 stroke section and look at FAQ section there is a link that will tell you how to jet the bike correctly.

 

I am not sure what an 85's compression should be but can guess it should be 120-130 PSI maybe more. If it is below 100 that is  too low.

 

good luck

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ok tonight i started the bike got it warm and then did a compression test. using a brand new matco tester is showed right under 130. figuring that wasnt the problem( which it still may be the problem}. I then pulled the carb and although dirty on the outside pretty spick and span on the inside. I could clearly see through all the jets and holes ect. I do have the carb soaking in carb dip but i dont think that is the problem. the guy i bought it from said it ran fine until 2 weeks ago and it started acting up so i would think the jetting would be ok. check out the video and let me know what you think.

 

 

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Ok one at a time I have cleaned carb, changed plugs, changed stator and fly wheel. Still exact same problem. I also tried the wd40 and now I have a wel lubricated bike lol but no change. Please advise

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Comp on a yz85 should be 120 at minimum.

Build a leak down tester from my thread to check for air leaks

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