Only other thing is probably leaking crank seals causing it to run lean and hot.This can cause a piston seizure.Replace the seals and see if you can salvage this top end.Plus don't overlook other things that can cause it to run for awhile and then die like a kinked fuel tank vent line.

 

Is it straightforward as far as replacing the seals? I've narrowed if to actual heat seizing because when it quits the starter either clicks or won't crank it over until it cools a little bit.

 

Also is this the correct part number? I don't want to order the wrong ones 0450017

 

0450017 and 0450018.Dirt Cheap Yamaha, Honda, Arctic Cat & Polaris OEM Parts & Accessories – Cycle Parts Warehouse

 

Ok I pulled back apart and don't think I have crank deal problems after all. The aftermarket piston and cylinder kit I got seems to be off. After centering the ring in the bore it is butted up end to end. Thinking I got a bad one. Could someone help with the ring gap piston to wall clearance.

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Manuals don't show ideal ring end gap measurements,only if end gap exceeds .030 (way too much in my opinion) replace the piston/rings with over size piston. Best thing I can tell you on this aftermarket piston ring is that the full size 250 and a lot of other two strokes have a .009 to .018 ring end gap range for the most part. I would think this little one should have at least a .006 to .008 ring end gap when placed in the cylinder.

 

It was running fine earlier today the kids shut it off now it won't start. Took carb off cleaned it getting fuel and spark when you hit starter it'll act like want to run but will not, even tried to hit it with a little starting fluid still no help can someone please help

 

Spark,fuel,but wont hit with starting fluid,then I'd check compression.

 

I replaced the entire top end last week got it running was running good until today they shut it now nothing could it be crank seals by the way it's an 06 sportsman 90 2 stroke

 

Could be seals,but I'd check compression first to see where you stand. Contrary to what people think,you can loose compression if a seal pops out or leaks bad enough. Has to have a good sealed bottom so you can create enough vacuum to draw in fuel and air,compress it and shoot it up through the transfer port to the top of the piston.If compression is below 100psi on a new top end then you could have a ring seized.On seals the most common one was behind the stator on these 90s. Read this post on a similar problem like yours. Seals were the problem.https://atvconnection.com/forums/kid...ml#post3317510