I have a 1980 Honda Express 2 and it is running great now that I cleaned the carb out, but it isn't running very fast for how good it sounds. I can only get it to about 25. When it gets to top speed I can feel the clutch grab the next gear and I get a surge of power and then when I reach about 26 mph it drops a gear and goes back down to 24 mph. How can I make it stay in this higher gear? I feel I could be getting close to 30 if it would stay in the top gear. It's been suggested that I may have too thick of transmission fluid, but I bought the bike with only 127 miles on it, so I imagine it to be the original fluid. Maybe it just needs some new clean fluid? It has also been suggested that I may be running too rich, so I moved the c-clip on the throttle cable one notch with no change. I also grilled the muffler and still nothing. Anything would help!