Condenser is Also nearly brand new. I'll try one from a different engine anyway just to rule it out. I'll check the points and timing too, would I be better off switching to electronic ignition? I have everything for it already just havent done it yet. I haven't checked the spark straight after running it, but it does still have spark. Will switch he plug too.

Uploading pics doesn't seem to work from an iPhone. If I remember I'll upload it from my computer later. Basically all ive done is replaced the shaft the throttle plate pivots on with a more standard one so it is actuated like a normal carb not through the 90 degree gears. Exhaust is just a straight pipe to replace a baffled muffler. And the carb seems clean, jet is at least, it runs normal for a little bit so it's likely no that, I'll give it a look over still.

You may have seen the kart, there's photos of it on diygokarts, pretty sure your a member, I'm jman231994. I was reading somewhere that a faulty coil can fail when it warms up? Could that be it?

Thanks for the help