I just put a new top end in a 76 Honda MR250 and it runs terrible. It starts hard when cold and hot. When it does run, it backfires out of the carb when decelerating like a lean engine, but then has a completely black plug. Idles somewhat well and torque is good low end. Top end torque is terrible. Im running 23:1 gas. The carb is a 36mm Keihin. Floats at 20mm, main jet is 110, slow jet is 48, the large idle screw is 6 full turns from bottom and the small mixture screw has .8 stamped into it and is 2.5 full turns from bottom. I live in Iowa, elevation is about 1000.
Another thing is a constant flow out of the overflow valves on the sides of the carb, im not sure if its the floats or what but the needle under the floats seals well when i blew through the gas line inlet.
The bike is running with a UNI air filter, no air box. And there might be a few cracks in intake boot coming off cylinder to carb but it is taped up. Should I buy the new boot then adjust the carb ?
Thanks for any help,