tyz250 carb and jets

[Gil Gallad]

in my infinite wisdom [or stupidity] i came across a good condition tyz250 engine, all complete except the carb. having mikuni vm carbs coming out my ears  ;D i wondered if anybody knew the standard jets for this engine? or at least somewhere to start?  i've got a vm26 of unknown origin with airscrew one side and tickover the other, which i presumed was off a single? also got vm28's off a gt250a which also fits the rubber carb adaptor. any recommendations which one to use? i'm changing the standard front sprocket for a 14 tooth and it definitely won't be used as a trials engine any more, it's going in a suitable road chassis when i can find one and an adapted rg250 spanny. many thanks.  8)
cheers, gil.

[Gil Gallad]

sorry, my mistake. the engine is actually a ty250z  and any info, apart from it's a pre powervalve model, water cooled engine from 1992  ;D
cheers, gil.

[tony27]

The motor was used by Scorpa for quite a number of years after Yamaha stopped building trials bikes, maybe do a search on trialscentral.com

[AAAltered]

This site has the parts lists for many TY variants.  If you see yours here, open the Model link then Carb link for that model.  Scroll down and it has the standard jet PN.

Interestingly the 1992 is not there, but the 93 water cooled is.  Is the prefix 4GG?  That appears to be the first water cooled in the list.

https://www.cmsnl.com/yamaha-ty250_model16818/

[Gil Gallad]

many thanks you two  8)
i'll give the sites a look over. i was told the engine was 92, but you could be right at 93. it's definitely water cooled. just wondering with it being a trials engine what sort of porting it would have compared to, say the yz250? i've found a 14 tooth front sprocket for it and with a 43 tooth rear it should put it on the same road gearing as my gt250's. looking forward to having a blast  ;D
cheers, gil.

[tony27]

Motor had no development for years, pretty sure when Yamaha stopped building complete bikes & just sold the motors to Scorpa they were the same as their first watercooled motors
Porting will be a lot milder, no powervalve means the exaust port needs to be quite low in comparison to a YZ

[Gil Gallad]

so definitely some scope for a bit of development? will build my own header pipe for it to start with and go from there. the jet sizes in the manuals are all over the place, but they'll give me a starting point. then it's onto the fantic 250 k roo engine for more fun and games  8)
cheers, gil.

[ststrider]

i have a 76 ty 250 with a 26 mikuni and i run a 220 main if that helps.

[Gil Gallad]

thanks for that. i'm going to try a 26mm mikuni vm on it to start with, but unfortunately the engine didn't come with a cdi, so i need help there. i've got a few suzuki cdi's, just need to know where the 5 wires go. 3 are bundled together, so i presume they go to the cdi, and the other 2 ditto, but will either go to the coil or the kill switch. still working this bit out. anyway, thanks for all the suggestions/hints/tips  ;D
cheers, gil.