Remember a few things when playing with the stroke on a two stroke engine:
1) The crank case volume is fairly critical. Bigger flywheels won't fit the
tight case walls and running a smaller displacement on a "big" case will make
performance suffer.
2) Stroke changes also change port timing, so not only wil the compression
ratio need to be fixed but the height of the ports in the cylinder as well.
This may not be as simple as raising or lowering the whole cylinder, as optimum
port timing is largely based on the amount of TIME the port is open, and this
varies with stroke and rod length.
3) A longer stroke may need the skirts trimmed to clear the flywheels. If too
much is trimmed then the bottom of the skirt allows the exhaust port to
communicate with the crankcase at TDC and power is shot. If the engine is a
piston port type (old tech) then the position of the bottom of the skirt is
even more critical for intake timing.
I may not know how to make 2 strokes fast, but I have tons of experience at
making them not go at all.
Simon Smith
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