If the bike is running well when cold and at high RPM it wont be leads, plugs, coils, needles or vacuum loss. The carbs on these bikes have an enricher circuit, what Yam call the choke. But it's not really a choke in the normal sense in that when operated in doesn't physically increase the idle speed by closing the throttle butterfly and acting on the throttle linkage. All it does in close off the air bleed on the pilot circuit slightly enriching the fuel mixture i.e. a choke effect.
This is controlled by small plungers which sit at the front of the carb, below the crab top just as it joins the induction rubber, as you operate the choke lever, the plungers are pulled out. These stick and you only need one not to return fully and you will get exactly the symptoms you're describing.
This is controlled by small plungers which sit at the front of the carb, below the crab top just as it joins the induction rubber, as you operate the choke lever, the plungers are pulled out. These stick and you only need one not to return fully and you will get exactly the symptoms you're describing.
Later