You may be blaming the chain for other problems associated with higher HP engines on karts.
The motor sliding back on the frame rails may make you think the chain is stretching.
The 1 1/4" axle flexing from the higher HP causing the chain to come off or damage sprockets.
Etc
Finally ran the big block with 428 chain 2 weeks ago at Roebling Road. No chain related issues. Cooked the clutch but I think it was a jackshaft ratio problem. The clutch wasn't spinning fast enough and felt like it kept disengaging. In one lap all four discs were fried. Damn.
The clutch is on the jackshaft. I will have calculate the ratio myself. I'm sure the problem is in the math. I run 4 stroke so I've never "stuck" and engine but it sounds super sucky.