COMO engines are re-branded SuperTigers. If your engine has the front bearing housing bolted on. You can rotate the front housing 90 degrees to the left and it will run backwards just fine.

Your engine, if I remember correctly, doesn't have a removable front bearing housing? So, unless you can find a left handed crank for a ST S51, you are out of luck in getting it to run backwards.

But, you can run a pusher prop. You can buy them at a lot of modeling places.

Your carb sounds like it is a Mark II or III Super Tiger carb and it is referred to as a twin needle carb. The needle with the compression nut is the high speed needle.On the other side of the carb there is the low speed needle in the center area of the throttle arm. This is not an air-bleed carb.

Enjoy,

Jim