IN a 2-Stroke engine the atomized mixture from the carburettor is sucked into the Crankcase on the up-stroke of the piston and forced via the transfer ports into the cylinder on the down-stroke. This process can be seen at the website http://www.keveney.com/twostroke.html.

In the 1970's, a popular tuning technique was to stuff the gaps inside the crankcase housing with Epoxy Resin to increase the Crankcase Compression Ratio in an effort to get more mixture into the cylinder and hopefully get more power.

On a Piston-Ported engine such as the VeloSoleX S 3800 engine without a Reed or Rotary Crankshaft Valve, the ideal Crankcase Compression Ratio is around 1.45 : 1. Any value higher than this and the mixture tends to get forced back out of the carburettor particularly at low RPM and also if the Carburettor Venturi Diameter has been enlargened.

Since the VeloSoleX S 3800 already has a Crankcase Compression Ratio of 1.45 : 1, it is NOT RECOMMENDED to improve this value further.