Model: GasGas TXT Racing 125, 2018

Carb: Dellorto PHBL 26 BS

I have just bought this bike & am struggling to adjust the carb so that it runs cleanly.
The fuel screw needs to be quite far out (4.5 turns) to get it to start reliably, & the idle itself sounds fine, but off-idle (bottom 1/8th throttle) doesn't pick up clean with this setting & the needle in standard position (3rd from top clip). If I drop the needle the pickup cleans up a bit, but at any needle setting the engine sounds raggy at around 1/4 throttle. Returns to idle ok & w/o pinging. Fully open it sounds fine.

Jetting is I think standard, but the needle looks scored & doesn't sit absolutely centred in the emulsion tube. Plug looks slightly dark but not too bad.

It's really just the problem in the pickup from idle & constant running up to 1/4 throttle - which is where I'm riding most of the time ofc. Means I'm having to work the clutch harder than I'd prefer.

Any advice on how I could tune this very welcome. Thanks in advance.

 

 

Is the air filter properly oiled ?

You need a bigger pilot jet. Try a 38.

 P.s  check a carb diagram. You could be missing the needle jet.

Edited August 2, 20224 yr by lineaway

5 hours ago, b40rt said:

Is the air filter properly oiled ?

Yup.

31 minutes ago, lineaway said:

You need a bigger pilot jet. Try a 38.

 P.s  check a carb diagram. You could be missing the needle jet.

Thanks for the tip. I've had the carb apart to clean everything - the needle jet is fine, as is the float level.

Check the reed petals are in good order and seating correctly. Check for exhaust leaks at cylinder joint. Many 125s are a bit gutless and lack pulling power at just over tick over, perhaps this plus a bit of wear. 4.5 turns out seems far too many

3 hours ago, robertslinger said:

Thanks for the tip. I've had the carb apart to clean everything - the needle jet is fine, as is the float level.

Sorry its the keihin thats easy to loose the needle jet!