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Help! 2006 yz250. New top end stop running.

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Put a new top end in my bike. Did two heat cycles( let it run with little throttle untell biked warmed up. Then cut off let it cool off and repeat.) When I started my third heat cycle I was going to ride it slow up and down the road. Started the bike, let it run for like 30secs.Then the bike just cut off. Took the spark plug out and it was wet. Took the cylinder head off and it seem to be a little gas on the top of the piston.(flooded maybe) bike has plenty of compression. The gas I have in it was a little old. Maybe two months old mixed 40:1. Also the middle gasket seemed like it was stretched out(maybe a blown head gasket.). Didn't fit in groved like when I first put the gasket on the first time. What could it be?

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One more thing, after all this when you kick the bike over. The kick starter would compress back up sometimes. Did not do this before bike stop running.

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When I break in a fresh engine I always start with fresh gas and ride it about up to 3/4 throttle for 15 - 20 mins get some load on the engine and get some oil and gas to the bearings. Have never had a problem. Let it coolants check it over then ride the hell out of it . letting it idle I just don't see the bearings beeing lubed properly and I would think a plug would foul out like that. Try a new plug and see how it runs

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Sometimes when my bikes are flooded or haven't been ran in a long time and have a lot of gas in the cyl the will back kick more

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Sometimes when my bikes are flooded or haven't been ran in a long time and have a lot of gas in the cyl the will back kick more

So what should I do to fix that? Take plug out and kick it a few times to clear it out? Thanks for the help

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When I break in a fresh engine I always start with fresh gas and ride it about up to 3/4 throttle for 15 - 20 mins get some load on the engine and get some oil and gas to the bearings. Have never had a problem. Let it coolants check it over then ride the hell out of it . letting it idle I just don't see the bearings beeing lubed properly and I would think a plug would foul out like that. Try a new plug and see how it runs

Ok thanks. I'm going to try some fresh gas and a new plug.

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Letting a 2-stroke idle until warm is a recipe for a fouled plug.

Not true properly jetting 2 stroke will never foul a plug no matter how long you idle it. Not warming up a 2 stroke properly is recipe for cold sieze.

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I have never ever fouled my yz250. I let my bike warm all the time. Your jetting is far off if your bike is fouling.

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Also the middle gasket seemed like it was stretched out(maybe a blown head gasket.). Didn't fit in groved like when I first put the gasket on the first time. What could it be?

i have found this happens quite a bit with the oem o-rings, they kind of naturally expand (probably from heat and pressure) after you put them in and after removing the head are a real pain to get back in, i find the moose racing o-rings don't expand near as much

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if the gasket touches fuel it will get soft and actually grow to the point that it will not fit back in the channel. let it dryoff for a few hrs . it will return to size. I accidently dropped one in my parts washer and had this happen. let it sit for a day and like majic it was back to normal.

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good find, ive never had this happen but i would imagine it would leave people searching for days

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