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Piston question

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I was riding my motorscooter which is a 33cc two-stroke engine for at least one to two miles straight while full throttling. Down the road I let go of the throttle since we were gonna turn around and then the engine shut off and I couldn't pull the pull starter as it was stuck. I was sure that I burned the piston but what else can you tell me that I did wrong besides full throttle for one or two miles. Here's a picture: http://home.earthlink.net/~abusive/images/DSC01443.JPG Thanks!

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What do you mean "made to ride wide open"? As for the picture, I zoomed in. I guess I just learned a new camera trick.

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my guess would be that you were'nt running enough oil. either that or it looks like you might have lost a ring somehow and it grinded up.

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thats definately a seizure of somesort,your cylinder is probably scored as well.as for what happened i would go over the basic stuff first.was your oil pump working or if you have to mix was it mixed right?jetting probably wouldn't be a factor on those things.mabey it was just a malfunction of some sort.those things dont last forever.i think what happened was when you let off the gas the slide was shut all the way and after bein run wide open it needed a decent amount of oil to properly lubricate it but did not get it due to the sudden drop of fuel/oil coming in and it seized.it is common on snowmobiles without oil injection.

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The piston shows signs of detonation damage, which is pretty amazing for a low-compression scooter engine. And it has a tremendous amount of blow-by stains on the skirts.

I'm inclined to agree with Crf250r121, it appears at first glance to be a lubrication-related failure.

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Alright, yes the cylinder was ruined as well and I took the piston rings off so it wasn't missing any at the time when the incident happened. Anywho that was about a few weeks ago, I bought the cylinder and the piston and the piston rings and now the scooter runs fine. Thanks, I'll make sure that I mix the oil with the gas correctly next time.

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No, I used old gas and new oil. Ran fine until I held the full throttle for a long time.

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That is an oil starved piston. I have done that a couple times on a smoker. When you chop the throttle you deprive the engine of lubrication and it locks up. On a MX bike you just pull in the clutch until you get back on the gas and it's all good.

I'm curious why the scooters clutch didn't disengage when you let off the gas, I'm assuming it has a centrifugal clutch right?

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No, I used old gas and new oil. Ran fine until I held the full throttle for a long time.

When gas sits around and goes thru temperature changes its octane falls off. Especially in cheeper cans that allow air in and out as the expands.

If you never ran it that way and this was your first time out I'd also back out the H screw on the carb. (High speed jet)

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Someone else posted a while back that if you run a 2-stroke wide open, then immediately close the throttle, the engine is still turning at a fairly high RPM for a few seconds, but the carb slide is closed so it is only getting the fuel it would get if it were idling.

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