It`s a 1973 501 motor in a 1974.5 GP frame. It has reed valved induction. It has a Euro dirt alum. swingarm, alloy rear hub, pro taper bars, progressive front suspension, and going to have Ohlins rear shocks. The motor has been ported to the Maico factory `HOT ROD` specs.(the same as what Adolph Weil had on his) This bike should be a real handful ! It is a true 31 cu.in. size.and should be somewhere around 60hp. Attached is a comparison between a 50cc piston and the 501. Interesting.....Dave.

Nice job, Dave!