Aye Tony,
Welcome to the TC Forum.
You need to make a visit to the TW200Forum! Link:
Yamaha_TW200Forum_carb_tuning I am sure you will be able to interpret the wisdom, even though you have a 125!?
Here is the link to Fowler's parts diagram for the 2003 TW125 carb:
2003_TW125_carb_parts_diagThe sound advice from the TW200Forum is "be methodical, make one adjustment at a time and test before making another, sorting out the top end first (Main jet) might be advisable" and have you a 'standard' air filter and exhaust fitted or something else?
These will also make differences. Usually, the factory 'set up' is the best, if you are running a 'standard' machine. If you have fitted a freer flowing air filter then you are likely to have weakness in the carb mixture throughout the throttle range and a standard silencer might be too restrictive to allow the engine to take advantage of any modifications to the inlet side of the engine. However, just fitting a less restrictive exhaust can also weaken the mixture from a ΒΌ throttle opening onwards, so the necessary adjustment needs to be made to the various parts of the carb affecting each stage of throttle opening, not forgeting that all four different stages (pilot jet, needle/needle jet size, throttle slide cutaway size and finally main jet size) have overlapping effects.
The whole set-up can be a "Dark art!" or a colloquialism for being a "pain in the neck"!
Hopefully, you'll no desert this TC Forum!?!
My regards, Bill