My cousin is asking for information on how to bump his TY175 to 200(ish). I searched and found a couple threads but none were specific.

1. What piston is used and are there any modifications to it?

2. I have been told there is a spacer under the barrel. Are there specs on the thickness?

3. I believe there is at least one UK supplier who can do said conversion but we will be looking to do this locally (if possible).

4. I told him to go on a diet or get a TY250, so far both of those suggestions have been ignored...

5. I'd suggest trying a boost bottle first but we'll see how that goes.

Any other tricks?

Dave, there are a few different pistons you can use. The cylinder spacer is to compensate for the different gudgeon pit height of the new piston compared with the TY175 piston (the top surface of the new piston must be at the same height at TDC and BDC as the old piston)

A popular choice is to use a TY250 twinshock piston. Another you can use is the KDX220 piston. Another is from a Yamaha Blaster (I think) quadbike. The TY250 piston has a bigger diameter gudgeon pin so would need the pin holes sleeved down. Can't remember about the other pistons re pin diameter.

The cylinder will need to be resleeved. The crankcases will need to be machined out to fit the new sleeve OD. I don't know what other people do with the head but mine was machined to suit the new bore diameter.

A much easier route for better TY175 trials performance is to take a bit of weight off the flywheel and fit a very thin head gasket.

Top end performance can be improved with a bigger carby but at the expense of some low RPM throttle response.

Bob Ginder at B&J (bjracing.com) does a kit. I think it went to 192 or 195 cc.

Several years back I was looking, he told me generally not really recommend it as it becomes much more noisy, less cylinder thickness and reliability, and not much gain. He recommended just overboring to the max, 180-185 cc I think. Bottom line, I just left it as is, did reeds and general port cleanup, nothing fancy.

kcj