Zenoah engine problem
 

With my second Marder I'm having problems with the engine. It starts easily, and runs fast for about 2-3 minutes, but it then bogs down and the car tootles along at a much slower than usual zippy speed. I've changed the carb from the other FWO Marder and this one still slows down after that 2 minute period. So it's not the carb. It's also not the carb gasket.

I think the piston ring or head could be at fault. I could buy a new piston ring, but the head internal liner thing could be damaged too. Do you think a big bore kit should fix the problem? (since basically new engine)

I've had no problems with my first Marder. Both Marders were second hand, and I think this second one was duff perhaps previous owner knackered it running it lean when new or incorrect petrol/oil mix :( a new engine will cost £200, which I'm not too happy with.

thanks for any help.