I just did a shifter kit a few weeks ago. With my old bike it's a 5 speed and I went with a 11 tooth counter sprocket. If a 12t were available I'd go with that. The first 3 gears are still too low, so I shift 1-3-4-5. It finally gets to 31 mph comfortably with a stock engine. (80-66cc?) Soon I will start to try to tune it. I dropped the carb needle down to the top notch and it helped. It still tries to 4-cycle a lot, so after I get this tank of fuel emptied, I'll go 24-30:1 and try that. It may do a comfy 35.