40 ~ 45 MPH is pretty good depending on your weight , I'm over 200 # so I'm always pleased ti hit 43 or so on the flat these days .

If you're not over 2,000' elevation , you can slip a thin flat washer underneath the carby slide's needle clip to richen it up a tad , if that helps , go up one size on the main jet of just leave the shim in .

Be aware that this will make the engine run rich and ' blubber ' when you get up in the mountains ! .