Mini Rok cutting out

Gidday brains trust I’ve got a Vortex mini rok that suddenly decided to be hard to start (hand over air box) and will run for a minute of two then will start stumbling on acceleration & stops. Cleaned and checked carby, jets and float, new carby, fuel, spark plug, fuel lines & swapped fuel pump. Unknown history on engine. It’s been running well for last 4 months I’ve owned it no issues. I did hear a bang when kart was in middle of track on weekend but no obvious body damage. Was wondering if it’s internal even though the engine isn’t making any crazy noises? Got me scratching my head…

Yeah that’s a head scratcher. Thoughts….

When you did fuel lines did you also do the pickup in the tank?
Can you see fuel being delivered to the carb?
Maybe pulse line or hole is clogged?
Ignition failing? (monitor RPM in data logger and look for any weirdness)
“Bang” makes me think you possibly have an air leak and it caused a backfire.

Plugged exhaust.? Reeds?

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Didn’t even think to use the data logger but that’s a good one to remember :+1:. Tank line checked and fuel getting to carb. Lots of air bubbles on start up but goes away. Will investigate pulse line. Engine has backfired since problem started so definitely could have been the noise we heard. No reeds on this engine (i think). Took the exhaust off to check bore and compression test, all good and 120psi. This was a sudden problem so not sure exhaust would be the issue but will clean it. Have ordered a vaccum/pressue test kit to do leak down test. I’m new to 2 strokes but maybe a crank seal?