I want to make myself a pitbike out of a JR 50 because i want the ease of maintenance of the 2 stroke. I want to raise the compression up to the ratio of a normal bike. 190 psi. Is there enough room inside the head that it can be milled down far enough that it will give that compression  but not have the piston hit the head? I will also put on a large carburetor and make the intake manifold larger for easy breathing.

Yep! There is a raised area on the head that can be shaved down and bump up the compression. I have the head off of mine now if you would like a picture of what to shave off.

That would be great. How high does it raise the compression?