I am not sure what you mean by the manifold paper. Do you mean the gasket on the muffler or the seal between the carb and engine maybe? As far as muffler gaskets, I never put those on and use rtv in its place. That shouldnt make any difference one way or the other. However, if you dont have an tight seal between the carb and case that could be a problem.

You wont necessarily see dirt in the carb. Wash it with some fuel. Then get a syringe and attach a piece of fuel tubing to it. Attach where the fuel tubing attaches to the carb and blow it out several times.

If the engine ran fine on that fuel before it should run fine on it now. I was wondering if maybe the can you are using has gone bad. Like it was left open or in the sun, etc.

There are a lot of things it could be. You just need to start with the simpliest things first and one by one eliminate potential problems.