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Alrighty, sweet. i drove it last night for the first time after idling for 15 min and blipping the throttle like you did every now and then 2 times. I pretty much did exactly as you said you would do but i only ran it once so i need to do it again for a little longer with a little more rev. So you're saying that after 25-30 hours you should replace the piston and rings?

Thanks for all your help im sure ill be back on pretty soon when something else breaks.

Todd wrote:...... So you're saying that after 25-30 hours you should replace the piston and rings?.....

I'm not saying that at all, Yamaha is saying it. Or I mean to say, I bet that's thier timeline. If not closer to 20 hours. They listed the life of my old YZ125's and 250's at 25-30 back in the 80's and 90's. I can easily foresee them wanting 10-20 hour rebuilds on thier little 80's. They will have listed it in thier manual someplace.

I would say, rebuild the top-end when you notice a significant (to you... your the one this thing is hauling around) power loss. Confirm with a compression test or a leakdown test if you have access to the right tools for that. Then drop the coin on the parts.

well i went and ran again last night for about 15 min, and i gave it a little more power than last. although not as bad, when i would open it up all the way, the rpm will climb and then drop off as if i was having blow by then i let off and put it back down it goes really strong. should tinkering with the air fuel mixture screws help?

If this is happening at higher throttle and rpm ranges, then the idle/air mixture is not the problem. It is probably the mainjet and/or needle setting messing with you. I'm guessing it is rich from your description, but you're not going to get real accurate diagnosis without having the actual motor there in front of the guy making the call. You may need to take it to a shop and have them fine tune the jetting.