Topic: CB400F carburetor problem(s)

[oldbob]

I just started the 400's motor after having the bike apart for the past five months. During that time, the only tune-up work I did was 1) set the valve clearances, 2) set the float levels, 3) check the emulsion tubes for cleanliness, and 4) replace the o-rings on the main jets. Otherwise, I haven't disturbed the motor since putting the head on 500 miles ago.

The bike started immediately and settled into an idle once the choke was off. Blipping the throttle produced smooth changes in engine speed.

A few minutes later, the idle began to climb, the carbs responded to the throttle as if they were significantly out of synchronization, and gas was running out of carburetors #1 and #2.

I suspect that the floats are stuck in a low position and/or there is dirt in the float valves. In the past, I have been able to "correct" the latter by repeatedly running the bowls almost dry and then opening the petcock. If the floats are stuck, I might have to pull the carbs, never a good time.

What I don't understand is how a rich condition (I assume that an overflowing carb is sending too much gas into its cylinder) would cause the idle to increase.

Any ideas?

Bob

[harisuluv]

Yes seems like you are overflowing. When you blip the throttle more gas goes into the cylinder and you g higher rev yes?  When there is more gas going to the cylinder from idle then you get a higher idle.

[oldbob]

I was confused because there would not be a corresponding increase in air flowing into the carburetors. Rather than seeing the engine speed increase at idle, I expected it to "choke."

Bob