yep, friction drive sometimes just wont cut it.
you could always try my old system of using 1/2" or 9/16" ID star washers on a shaft, ie...use a roller with a diameter of less than an inch! your tyres will love you for it, and youll accelerate...my husky 25cc used to hold 60kmh very comfortably with 1/2" ID washers... (about 7/8 OD, tangs to the outside, obviously...they stack to form a neat splined shaft thats easily replaced and CHEAP.) still suffer in the wet but. let those lil brushcutter engines REV! dont use kerosene or other strange things as fuel when strapped for cash!
the generic HT engine...if you took the time to read through most threads, you will find that theres sweet F all difference between different vendors, overall reliability is partially luck - partially skill. there are some that claim "such and such" and "blah de blah" but thats just marketing hype...
they are the best choice for a kit you can buy and know they will fit without any modifications, just some rather simple twiddling of spanners. maybe some tongue out the side of the mouth just so the missus thinks its hard or something...
the only choice is the 48 or the 66cc. some say bigger is better, some (like myself) have no desire to try a 66 ever again...
lets just say.... i dont carry tools when i ride a 48, seem to push home from forgetting to check the tank rather than any major issue, whilst my 66 for the week i tried it, didnt get me to work, or back home ONCE. i am biased
my opinion doesnt count.
other choices are using brushcutter/industrial engines either 2 stroke or 4... they dont fit neatly, theyre awkward, they all need these silly wide cranks... unless rack mounted, which makes the bike top heavy and very hard to handle generally. if you have ever used a pannier rack and put 10kg on it, then tried opening a gate while holding the bike, youll know what i mean.
some may disagree but once again, thats my opinion.
then you can think about all them extras like the expansion chamber (it ISNT, its a TUNED PIPE, an expansion chamber is simply a muffler of no specific size or length. meh. nomenclature. why worry?) on the twostrokes, etc...
