My OS 1.60 ran good before I put on a cline regulator, now I have 9000rpm high end and an idle around 1700rpm but no midrange. When I move the throttle to the center the engine dies. I,ve tapped the case and moved the tank over the cg,so there's no going back to a unpressurized system. I am running 10% nitro, with a slim lime pitts style muffler. Why is this happening?

Try Leaning out the low speed needle. If it's real rich it will do just what you say.
Dan

ASP3D My OS 160 done the same thing. (Simular setup) Keep leaning the low end. It was close to a 1/4 turn in to get to stop doing what yours is doing. Transistion is now reliable.

To adjust the low end, pinch off the fuel line at idle, if the rpms rise way up release and pinch it off again to make sure. That will tell you it is too rich on the low end. If you pinch the line and it just dies with no increase in rpm the low end is lean. There should be a slight rise, at least 200 rpm.

At the high end, pinch the fuel line slightly at full rpm until the engine either looses rpm or gains and then looses. I always fly 2-300 rpm rich.

What Brian said.. perfect