Cylinder mod for piston cooling

[StepVino]

Thanks mt. The pipe is a modded Next R with 20mm shorter header.
with the header joints cleaned up inside. It was giving me 11800 rpm
with a ported 50cc, that had less port timing than this cylinder.
I agree that a better pipe would probably make a big difference,
but don't know if it would be the biggest cause in rpm drop.
I did work out some numbers on the required header/flange size, and
came up with 1 inch, quite a bit bigger than it is now, maybe 3/4 inch
inside.

 

[Quanni90]

gotta hand it to you the cylinder is looking good !

 

[StepVino]

Thanks! I wish looks = performance. After all that, most I got
out of it was 10.2K rpm. Then I tried reducing the size of the
boost port by putting epoxy on the outside wall, and also lowering
the 'FDA' ports. Result was 9.2k max, and when I opened the
motor again, almost all the epoxy was gone. Back to drawing
board.

Then I tried increasing the main transfer channels by cutting
them all the way down as well:

That got me back to mid to high 9k's... Then I replaced the head
with one that had smaller squish band, raised compression from
118lbs to 140, retarded timing ~1degree, and lowered barrel
by using silicone gasket maker instead of base gasket.
Much better! Almost, if not all back to step 1 (10.2k rpm).

Now we've had a few fairly cold days, and I noticed noticeable
performance increase, so I should try one size smaller main jet.

It did an odd thing on a test run though. Porting should be for
around 10.5k, but when it gets to around 9.8-10.2k, it will quit
accelerating even down hill! Like the motor refuses to spin
any faster even when the load is reduced.