TY250 Mono pistons

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pbear62
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Bike: Yamaha TY250
Club: VMX Club of WA, AJS WA

TY250 Mono pistons

Postby pbear62 » Thu Aug 17, 2017 11:20 am

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
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Bike: Honda RTL
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Re: TY250 Mono pistons

Postby Gomey » Thu Aug 17, 2017 1:49 pm

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
Junior participant
Junior participant
Posts: 10
Joined: Tue Feb 24, 2009 7:08 pm
Bike: Yamaha TY250
Club: VMX Club of WA, AJS WA

Re: TY250 Mono pistons

Postby pbear62 » Fri Aug 18, 2017 11:00 pm

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
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Re: TY250 Mono pistons

Postby Gomey » Sat Aug 19, 2017 5:18 am

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
Junior participant
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Posts: 10
Joined: Tue Feb 24, 2009 7:08 pm
Bike: Yamaha TY250
Club: VMX Club of WA, AJS WA

Re: TY250 Mono pistons

Postby pbear62 » Thu Aug 31, 2017 12:01 am

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
C grade participant
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Posts: 32
Joined: Fri Aug 08, 2014 11:55 am
Bike: Honda RTL
Club: SQTA/LRMTC

Re: TY250 Mono pistons

Postby Gomey » Thu Aug 31, 2017 5:31 am

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
Junior participant
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Posts: 10
Joined: Tue Feb 24, 2009 7:08 pm
Bike: Yamaha TY250
Club: VMX Club of WA, AJS WA

Re: TY250 Mono pistons

Postby pbear62 » Thu Aug 31, 2017 12:21 pm

Fantastic - thanks for all your help.

Cheers, Andrew




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