Originally Posted by Kevlarr
I don't think 35-38 top speed is going to happen with a 40T sprocket. I have a 36T, a tuned pipe and a broken in motor and I top out at 30 which is plenty fast enough.
One thing I'm going to have to disagree on with Joe is the best oil is Opti-2.
I have no intentions of starting an argument here but I have a 41T sprocket, a 66cc Straight plug 6mm head stud engine and it's on a mountain bike, it will run 34-36 easy if you can take the massive vibration form those RPM's it will do 38mph if i'm on a slight decline, but 30-32mph is an easy speed for mine with mild vibration or I can back it down to 25-27mph with almost NO felt vibration at all.
these speeds have been confirmed by multiple vehicles and not just the digital speedometer on the bike, I will say that for a comfortable speed I would suggest the 40-41T for someone who is happy with the 25-30mph cruising speed it works the best for me at that speed range, but will run 35-36mph all out if you need it too, once the engine is broke in good and if it is tuned right, I dont have a tuned exhaust or a fancy carb. on mine either, I have a stock NT carb. and an exhaust I made out of 3/4 flex pipe and it has a small lawn mower muffler brazed to the end of it which I enlarged the holes in for better flow, flex pipe leakes and stays a little oily but works great for me.
The 41T is my favorite over all I have tried for all around power and mocerate speed. cant go wrong with this one in my book. I put a 36T on my other bike which has the slant head engine and it is slower with the 36T than my other bike is with the 41T.