I'm j opening a new topic for drag bike mike's question so that finshammer's topic doesn't get too cluttered.

Mike,s question:

Zevenenergie, taking that little moped from an 8K redline to 13K redline must have been fun.  Do you think it was choked off a bit with that 8mm carb?  That's like the size of a pencil.  I've got carbs that big on my model plane engines.  To run the engine up that high, did you have to switch to thinner piston rings?

I increased the cc to 73 and used a piston with thinner rings, but that isn't really necessary. This little engine went from 4 hp to about 15 hp and ran 100+ km/h with a variator drive and the lifespan is not really great.

And yes, that 8mm is a significant obstacle, but the biggest power gain came from the scooter exhaust I had installed. A 2-stroke is very sensitive to the dimensions of the exhaust.

If you put a standard exhaust on a 50cc 21hp 2-stroke racer, it only has about 6 hp.

More

I’m going to give some thought to using a reed valve on a four-stroke engine and modifying the camshaft so that the intake valve closes well after BDC, thereby achieving optimal intake timing and volumetric efficiency at any RPM. It would also completely prevent reversion.And perhaps it generates an interesting pulse effect in the intake duct.