Unstable Idle

I have an '86 yx600 Radian and since I bought it last may, the idle speeds up 400-500 rpm after riding 5 miles. Have changed the carbs twice, finally re-building and syncronizing the original carbs including all new rubber seals, o-rings, manifold boots and have tested all induction components with WD40, engine still speed up after a short ride.

In five miles in hot weather the air cooled Honda CB900C is finally warmed up and ready to shut the choke completely off. It is a fast idle setting on the carb end of the choke cable, not really a choke plate setting. The choke buterflys open first, then the choke cam lobe lets the idle down. You have to bend the choke cam lever on Hondas to set the cold fast idle. The main idle setting is a thumb wheel below the carbs, its hot in there. Hope your Yamaha setup is similar for this to help.

Theres no choke butterfly or fast idle cam on the CV carbs on the bike, the manual choke lever actuates a piston in a ported cylinder in each of the four carbs, there is no connection between the choke and the throttle butterflys.

I checked for air leaking around the manifold boots but there is none.

Theres no choke butterfly or fast idle cam on the CV carbs on the bike, the manual choke lever actuates a piston in a ported cylinder in each of the four carbs, there is no mechanical connection between the choke and the throttle butterflys.

I checked for air leaking around the manifold boots but there is none.