29mm mikuni

originally i had a 26mm mikuni copy i have now put on a 29mm mikuni and when i put the choke into the fully closed position the bike idles ok then decreases and dies
when i open it it starts to rev to death does anyone have any idea why because automatically i assumed too big a main jet but put in a smaller and all stayed the same and when i try to get the bike to idle normally it revs very little and dies any ideas or is the carb just too big for the bike ?


125 shineray

Sounds like the throttle cable is now too short and the slide is not bottoming out. Open the throttle and let it snap shut. You should hear the slide hitting the bridge in the venturi with an audible "click".
With the slide resting on the bottom you should still have 2-4 mm of free play measured at the twistgrip. Adjust this using the carb top and twistgrip adjusters.

This is assuming that your throttle stop screw is fully backed out. There should be no tickover at all with it fully unscrewed, then screw it in slowly until you obtain 1100-1300 rpm idle speed.

A 29 mm carb with a 125cc mildly tuned engine is a little too big. You might get a small power gain at wide open throttle but low down torque will be reduced due to a low gas speed through the relatively large choke/venturi size.

so your saying if i do that it will bottom out on its own and from there it should be ok i hope its nice and simple like that and where are the carb top adjusters?
will keep you posted many thanks for help from everyone mainly you forchetto without you id be bikeless (disaster) :scooter::thumbsup:

Quote:

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Originally Posted by my_bloody_shineray

where are the carb top adjusters?

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You might not have any, but they're usually on the point of entry of the throttle cable at the top of the carb, a threaded thing with a locknut on it.

thanks forchetto i bottomed out the cable and it idled a little hight and so i adjusted the idle mix screw to make it a little leaner which i am still fine tuning but seems to be working many thanks for your help forchetto

and you were right i dont have any carb top adjusters