Blown top end???

I own a 00 yz426. i love the bike, but last fall i blew it up. I was cranking around in a field, and all of the sudden it acted like it had no power, So i left off the gas, and it wanted to stall, i thought it was running out of gas but it didnt. It will start back up even now, but will not stay running and there is alot of scraping. I have not torn in to it yet, i just wanted to see if anyone has had this problem, and what it sounds like, i think its a ring i just wanted to see if it could be more then that. It doesnt have to much compression. I am also thinkin of putting a high compression piston and rings in, i wanted to hear what everyone had so say about that. Please help me thanks!!

If you hear scratching - your probably going to need a bore and cylinder replating :thumbsup:

I wouldn't start it again until after you tear into it.

yea i knew better the first time, but you get a few beers in you, and the story changes.. Any word about high compression.

High compression pistons are awesome. I've had one for a couple years and they really improve the off idle snap and midrange pull. I would recommend the Wiseco 13.5:1 piston. :thumbsup:

642MX, what type of fuel are you using for your 13.5:1?

642MX, what type of fuel are you using for your 13.5:1?

Citgo 110 octane leaded. It will run with pump gas, but it pings a bit.

I thought you couldn't run leaded gas in these bikes? Would premium with octane booster be enough or go with U4. Its almost time for a new top end and i was thinking Wiseco.

I thought you couldn't run leaded gas in these bikes? Would premium with octane booster be enough or go with U4. Its almost time for a new top end and i was thinking Wiseco.

You can run leaded fuels. Lead helps lubricate the valves, and leaded fuels are easier to dial the jetting in with. I've been using that fuel for about 3 years now. U4 is too expensive for me, and I wouldn't recommend the bottles of octane booster, they can cause some problems when used incorrectly. There is a company called Renegade Fuels, they make PRO102 race fuel that is unleaded. You may want to check that out if you don't like leaded fuels.

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