Looking for an Motor Repair

Welcome to the forum. Sorry you're having this problem but it can be fixed.

We're assuming you have a Chinese 2 stroke engine. That is the most common type.
It's always a good idea to tell us what engine you have when requesting help. There are many options as far as engines but if yours is the little Chinese guy, read on.

First remove the remaining nut and the exhaust pipe/muffler. If the stud is protruding, even a little from the cylinder try grabbing it with vice grips or pliers and turning it out. Rotate it counterclockwise.
If the stud is below the surface you might be able to grind a slot in it so you can use a screwdriver to remove it. A Dremel tool will work well for this.

Drilling it out is a last resort. You'll want to use a tool call and 'Easy-Out' and drill the hole perfectly in the center of the stud and only deep enough to get the tool to start, then screw the 'Easy-Out into the hole. They screw in by turning them counterclockwise. As it grips it will turn the stud out. They usually aren't in that tight unless someone has used a thread locking compound on it.

You'll need a new gasket and we highly recommend the use of a torque wrench. Set the wrench to about 60 inch pounds when tightening the fasteners. You can replace the studs and nuts with Allen head cap screws or order new fasteners from one of the sponsors here. Hardware stores will carry them also.

Good luck. Let us know how you do.

Tom