TY250 Mono pistons

[pbear62]

Hi guys,

I haven't been on here for quite a long time so my query may have been addressed previously - sorry if so!

I have one of the original 1984 TY250 Monos - red frame/steel tank model (#53Y) which is currently getting a
tidy up so I can have a play again next season.

My question relates to the piston fitted to these bikes - I have been told by a UK supplier that the piston from
a Pinky will fit with no mods & will make a huge difference to the way the bike runs. (ports in rear of piston
are different apparently?)

Does anyone here have experience with doing this - I don't really want to buy a new piston assy to find that it
doesn't work & haven't got a Pinky piston I can look at to compare either.

I'm also tidying up the ports in the barrel as per Stan Stephens (UK tuner) in an effort to sort out the rattling &
clanging that these motors suffer from.

Thanks in advance for any info, Andy

[Gomey]

Hi,
I have done the piston mod 3 or 4 times. From memory it is only the piston crown that is different. It makes a huge difference. Carb had to be re-jetted to suit along with the airbox lid to allow it to breath better.

[pbear62]

Thanks for that Gomey, Did you do any work on the ports or head or did you just fit the Pinky piston assy?

Cheers, Andy

[Gomey]

I just cleaned up the ports by smoothing them out. Nothing too drastic.
- from memory the top/crown of the piston is shaped allowing better gas flow to ports.

[pbear62]

Thanks Gomey,

Did you still have the original TK carb or had you replaced it with a Mikuni?

If it was the original one, where did you get bigger jets from? Yamaha only list a couple of different sizes & of
course they're silly prices too!

Cheers, Andy

[Gomey]

I kept the original carb and used a jet reamer to enlarge the jet. Didn't take much. Jet reamers are available on eBay.
Mark.

[pbear62]

Fantastic - thanks for all your help.

Cheers, Andrew