Basically the same engine we use in one of my wife's race bikes...just a 72cc version...uhh..with a 4 speed close ratio gearbox, ball bearing camshaft, oversize SS valves, ported head, Kitaco Mag/CDI, 20mm Keihin PE carb, Kitaco race exhaust, Takegawa oil pump, Kitaco crankshaft, Kitaco race clutch...and a few other goodies. In an SL70 frame, MB5 front end with CR80 wheel and rotor, Pro-flo clip-ons, extended swingarm, NOS Mulholland shocks, Michelin race tires, Excel rims, etc.
But other than that....it basically is a Honda Cub.
Goes pretty good, will do about 70-75mph flat out at 12,000 rpm. Wife has won a couple of championships on it.
This winter it will go through another round of modifications. Maybe a new close ratio five speed and a bump up to about 81cc.
Our vintage club has about 30-35 guys that race in the "50cc" class...which includes four classes that run from 1967 and older 50cc only, all the way up to modern 75cc water cooled two strokes.
Here's a couple of vids of her kicking butt at Loudon (give them a minute to load, the server sucks).
That was the first bike I ever rode.
I was 10 & I was at a relatives home in Iowa.
They owned a dealership & had one in the garage.
I found it...
I rode that thing empty. All day long.
It was Red as well.
That race bike looks like a OHC aluminum head motor. The old cubs were cast iron heads with pushrods.
Ok now, let not get picky....I've only built a couple of dozen of these things, including C110 iron head engines, OHC engines, C90's, C70's, XL70's, SL70's etc.
Pretty sure CURRENT cubs are OHC.
Feel free to peruse my world famous website about building vintage honda single race bikes. http://www.jrbranson.com/HondaRacer/mainpage2.htm