Malossi Holes in the USA

We keep burning holes in the top of 210cc Malossi pistons when using the “SiP” left hand pipe and running 24/24G carbs they are jetted right and the timing is set to what is recommended … BUT still they drop a hole in the top feathering off to the exhaust port the only difference is that we run USA specification heads with the different combustion chamber TELL US the parts are not Cheap! This only happens with the Left hand Pipe
K. :0[

maybe the carb is still to lean. recommended size would be in my opinion 132-138, if you are near sea level even higer. I prefer a 26 or 28mm carb.
try also a W2CC spark plug and a thicker head gasket.
test also another pick up and ignition box to see, if the problems come from a damaged iginition.

rgds, alex