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Carb tuning question


robertslinger
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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.

 

 

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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.

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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

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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!

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