I just installed an engine that was recently built and tuned by chris at benchmark, It is a 686 with cams and valves and minor other mods and a Mikuni flat slide carb. It is running a dynatech cdi. Under load it cuts out as if it had a rev limiter. After the RPMs increase it runs great... it doesnt seem like a carb issue... it feels to consistant and acts like an electrical or ignition problem. Does it more as it warms up. when I tried to ride it as it got hot I had to be on flat to get it to go, or even a little down hill.