First rebuild? Please help!

Hi, I recently bought an 03 YZ85 off of craigslist and the price was too good to pass up.. it doesn't run and it has some weird things missing like a rear wheel spacer but anyway, it feels like it doesn't have a whole lot of compression. I can push the kick start lever with my hand. I got a compression tester today from autozone and it gave me a reading of 130psi. I'm not sure how accurate that is but from what I have heard that is on the low end. What would you guys recommend doing in this situation? I already pulled the cylinder off and the piston looks alright it has a good amount of carbon buildup on the top but no marks. I have worked on bikes a little before but have never rebuilt anything. Do you think that putting a new top end kit on it would get it running? Any other suggestions? Thank you very much for taking the time to read this and I would appreciate it if you helped me



Throw a new top end in it. since you already have it apart... double check your jetting specs also while your in the carb make sure that your float needle and needle seat o ring (if it has one) is in good shape (half the bikes i take apart these are bad) and start at stock and go from there. get a manual too for the bike if you don't already have one.. it has a lot of information that will help you a lot in the rebuild process... while your in there make sure there is not up and down play in the crank rod. then go from there...

Based on that piston your jetting looks good.

When trying to diagnose the no running issue, you need to go back to basics. Spark, fuel and compression. 130psi is a bit low but probably enough to start it, plus I imagine once you put in a new top end it will be fine. Clean your carb, try a new spark plug, put in a new top end and go from there


Thank you, I ordered everything last night, hopefully I will get it running soon

I'm going to be putting my sons back together when the cylinder/head get back from Mr. Gorr... my first real 2 stroke rebuild... it was a fresh top end... (could still see the honing marks on the walls... when I put it back together should I lube the rings or anythihng or just torque it correctly and fire it up?

YES, coat your needle bearing, cylinder, piston and ring with the two stroke oil of your choice.

OK so like my post above says going to be putting the boys YZ back together today, do I need to do anything to the gaskets? RTV? anything? or just put it together? what about warm up and break in procedure, I'm an XR guy so this is 2 stroke stuff is all new to me... thanks in advance...

Edited by delirious_nomad

Little bit of grease on the head O rings. Little bit of moly oil on the powervalves (a little 2 stroke oil will be fine if you don't have moly oil). Speaking of powervalves, use some medium loctite on the small powervalve shaft screws.

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