Author Topic: Yamaha 125 carb  (Read 486 times)

Tony

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Yamaha 125 carb
« on: August 29, 2018, 08:53:15 AM »
I recently raised the needle in the carb to give slightly better performance and it worked to an extent. However I now have a flat spot at low revs and seem to need wider throttle openings. Any suggestions, maybe a different profile needle. It's a 2003 TW.

timbo

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Re: Yamaha 125 carb
« Reply #1 on: September 15, 2018, 06:18:43 PM »
Come on fellas. Can anyone help out with some sound advice  ;)
Namaste

themoudie

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Re: Yamaha 125 carb
« Reply #2 on: September 15, 2018, 11:12:12 PM »
Aye Tony,

Welcome to the TC Forum.

You need to make a visit to the TW200Forum! Link: Yamaha_TW200Forum_carb_tuning  ;D  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_diag

The 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
« Last Edit: September 16, 2018, 08:11:35 AM by themoudie »

DoubleDiamond

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Re: Yamaha 125 carb
« Reply #3 on: September 19, 2018, 08:29:47 AM »
If you want a little bit more performance from a 125 then maybe fit a big bore kit?  Tweaking the carb will only make marginal differences when you have only 12bhp on tap in the first place.

Tony

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Re: Yamaha 125 carb
« Reply #4 on: September 24, 2018, 05:41:14 PM »
Thanks all. I am taking your advice and fettling. I think the best solution is for me to ride my cb400ss instead!