Is this a Q42 Or 35?

Stick a popsicle stick through the ex port till it touches the cyl on the oppositeside. Turn the crank till the piston pushes on the stick enough to make a mark on the stick. ,35 is 1 7/16 bore. If it measures bigger than that ,it's a 42. I forgot what the 42 bore size is. Externally, they are identical.

Should be a part number on the bottom of the crankcase- you may find the numbers 42, 35, or 41 (for US engines) somewhere in the number.

Single piston ring, 35cc or later model 40cc or 42cc. I have the 35 and 40cc version both early style. Is there a black wire coming from under the flywheel opposite side of the carb? If so then it's a point type ignition 35cc. If not it will most likely be a newer 40 or 42. A bore measurement will confirm this.