do I have to run the muffler on the ys 110 or can I just run the manifold from the engine without the muffler??

The muffler will only affect the noise of the engine. Not the performance. It will be loud though. Any reason why you don't or won't run a muffler?

Dennis

just easier to work with. its hard for me to get the cowl on with the muffler installed and i like to keep the plane as clean as can be.

it'll work but it will be loud. probably anger the noise people at your local field without one. any room at all for a pipe down the bottom of the fuselage? if there is you could run a Johnson header and a Mac 3.5cc Quiet pipe.

Dennis