Topic: CB400 Carburetor problem

[tetleydatsun]

Hello everyone,this carb will surely be the death of me.
Firstly I have rebuilt everything on this bike and have used the old brass in the carbs,the bike runs fine except when it warms up the idle creeps up(Sucking Air I thought)new intake manifolds,slightly better. The air screw on number one carb does absolutely nothing,if I screw any other in to seat the bike wants to die and if I put my hand over the carby (number one)the bike just keeps on running.I have changed the carby and has made no difference at all.Tappets are correctly adjusted.I'm stumped.

[HondaMan]

Have you changed out the O-rings in the intake manifolds, where they fit against the head?

[Mark1976]

  The air screw on number one carb does absolutely nothing,if I screw any other in to seat the bike wants to die and if I put my hand over the carby (number one)the bike just keeps on running.

Got spark?

[Deltarider]

Tetley, we need some more information, I'm afraid.

the bike runs fine except when it warms up the idle creeps up

After a cold start and when you have reopened the chokes, at what rpm does the engine have a good idle?
The air screw does nothing, you say. At what rpm did you test?
Are you sure it's not sucking air, like between the manifold and the head?
Just to be sure: advancer moves freely and works as it should?
I take it you do not have any airfilter at the moment. What's the result when you close the chokeflaps partially after engine has warmed up?
Are you aware Honda lists two optional different sizes slow jets in the CB400F parts list?
Tip: do some more posts and after an x number you can post a video with sound.