
So, Chrias and Just For Kicks, did you ever finish your pocket bike engine projects?
Now that final exams are over, I'm working on two pb engine projects. One is a moderately modified 47cc on an old cruiser bike with 17-tooth rear sprocket. The other is an unmodified POLINI 4.2hp motor on a SCHWINN SKYLINER with 7-speeds.
Both will run thru the bikes' gears on the right side. My biggest setback is finding/using the correct chain without a jackaxle. Another sticking point is acquiring the correct sprockets for proper gear reduction.
Gear ratios are VERY stiff. The SKYLINER will have 65:1 in first gear

, and the old cruiser geared at 33:1.
Speeds at the Italian engine's peak torque(8,000rpm) and hp(11,000rpm) ranges should be 24mph and 33mph, in 7th gear.
On the old bike with single sprocket, peak torque and hp arrives at 20mph and 27mph.
Top speeds are reasonable, but acceleration should be quick...and brutal.
Plan your work, then work your plan.
Myron