Re: Sprocket question.
I have one bike with the straight plug 66cc engine and have a 41T sprocket on this bike.
I also have a bike with the slant head 66cc engine and have a 36T sprocket on it, my slant engine pulls the 36T as good as the straight plug does the 41T and the basic difference in the two engines is that I shaved the head a bit on the slant engine and added one of Manic Mechanics ported intakes, all else is the same.
I weigh 2 bucks and a nickle and they both pull me just fine on the hills in my opinion as long as they are tuned properly, tuning is very important, if the engine is running rich it will not pull hills worth a darn in my experience.
I say the 40/41T is probably best all around for most but with my 36T I can cruise real nice at 32MPH with very little vibration, the 41T bike will only cruise with low vibration @ 25-27MPH above that it is wound up pretty good and gets very uncomfortable in a very short time.
Personally I think if someone made a 38T that would be the most perfect all around tooth count and would probably give a nice comfortable 30MPH cruising speed for most riders and still do plenty good on moderate hills for all accept the Big ole Boys.
If you are 150lbs I say get a 36T make sure your engine is tuned very good with a better than stock exhaust and get one of the manic intakes and be sure you have an NGK B6HS sparkplug instead of the stunk one.... (Stock/Junk)
I plan to go 36T on my other bike as well when I get the manic intake and a better exhaust on it.
Just my opinions....nothing more nothing less......!
Good luck with what ever you deside, Peace