MOPED ARMY

I'm looking into doing this properly since I have all winter.

At least on mine, there's a nice ridge in the intake port that could use some cleaning up. Looks like it would clean up nicely to about 20 or 21mm.

The Metrakit 65cc has some huge ports. I had a 16mm intake manifold from somewhere, and it looks like the internal cross section at the bend was less than the stock 12mm.

Since the ports are so huge, i'd think this engine could get enough airflow at high RPMs to make good use of the 21mm carb, as long as there aren't restrictions elsewhere. At low RPM, there's not a lot of air velocity through the carb, but I think the PHBGs are supposed to be pretty good about that if they're set up well.

I think with this cylinder, the main restriction is going to be the matching of the case to the transfer ports. With the transfer ports fully open, the back of the piston is about 10mm into the case, and past 10mm (at least with the ZA50), there's not a lot of metal there to remove, unless you do some build-up welding on the other side.

I think for the 80cc kit, you'd also have to bore the hole bigger just to get the cylinder to slide into the case...

I have plenty of room for gasket to seal on mine, and I matched it perfectly. Which gasket did you match it to? The metal gaskets are a little wonky.

Also, 21mm is fine, if you want to open up your intake to match the 21 that would be ideal, but running 21 into 19 isn't a big deal.

I usually run all three metal gaskets and the paper gasket, I've had head clearance problems otherwise, but that has just been my luck. Also, you don't really want to polish the intake side, leave it some what roughed up, it aids in atomization