2 stroke compression ratios+

[motodio]

I am currently working on my 1975 GT185, looking for more torque (if that's possible) and learned in the 4 stroke world higher compression serves up better torque, with some modern-day motors running as high as 13:1 cr. I suspect the same is true for 2-stroke motors.

When I was in college, I owned a Zundapp super sabre 250cc single, pre-mix. I played around with removing the head gasket and sealing the head to cylinder with aluminum paint. It seems to seal and run fine, never noticing any detonation. Couldn't be sure if it increased torque but I thought it did.

So now I take the GT185 out for a ride after 40 miles and after returning home, I notice the left carb is now leaking fuel and the generator lite is on (gotta love those old machines). I make the necessary repairs and at the same time put the Zundapp fix on the GT. The increase in cr is noticeable as the elec and kick start provide more resistance.

How do I know if I've gone too far? Since I'm unaware of anything but stock head gaskets (.042"), to get something smaller I'd have to make some from copper sheet, maybe 0.20".

Comments

[Coyote]

A common 'hop-up' is to use the correct gasket and mill 20 off the head. Another trick is to shim under the cylinders to raise the intake and exhaust ports. Due to the piston port induction on these motors, I don't think any true high compression is obtainable. On a Yamaha maybe as they use a simple reed induction. A glorified chain saw motor.