ORIGINAL: Rcpilet

Grip the front of the engine with your hand and put your thumb over the top of the carb. Squeeze it down on the motor to compress the O-rings and seal it up good. Now tighten the bolt to hold it in place.

You just need to get that carb down in there TIGHT and get it seated on the O-ring or it will never seal.

On the muffler attachment -- just cut 1/4" (6mm) off the allen wrench. Then it fits in the tight spot and makes it easier to attach the muffler. I don't like the muffler attachment either. Small price to pay for such a nice running engine though.