I've tried everything I can think of, even bought a new big bore kit for it. Got everything hooked back up and it runs great for about 8 to 10 minutes then stalls like I hit the kill switch. One it cools it starts right up again.

Its oiler is removed and capped, I mix the gas manually.

​​​​​​Any help or advice much appreciated
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"Won't turn over " means seized, is this the case?

 

That is correct. I found it is running very lean. I lost a little compression but it it still around 108.

I pulled the in line fuel filter. The I Put a bigger jet into it. It was a 92 and I put in a 100. Waiting for a new seal to test out.

Weird thing also is when it overheats the kill switch stops working. Here is a video when the throttle stuck open on me.

I've since replaced the starter assembly but still having issues with turning it off. I'll hit the off and it stays running until I touch the gas.

 

What oil to fuel ratio are you using? That is a 1980s engine, designed when oil to fuel ratios were high. The Linmax copy of the LT50 used pre-mix, and specified 30 to 1 ratio. Can't help with the "running on" problem. A hot spot in the head can turn an engine into a "glow plug" type, not needing a spark to run, but that seems like the plug is getting power. Try whipping a thin lead to the coil off, if it does it again and see if that stops it. There were two different types of ignition systems used on LT80s, but both short the power/trigger lead (black/red) from the magneto, to earth, to kill the spark.

 

It's the top end. China stuff. and it's 89.167cc's.. ppl lie.