Z1B Carbs overflowing, normal but unusual ?

[ian_2020]

Hi All,
As it says in the title, my carb No 2 (counting from kick start side - is that the right way?) is overflowing via the overflow pipe. I think this is down to the usual suspects of sticky float, gunge, etc. What's seems a bit strange is that when the fuel tap turned on, there is a delay of about 30 seconds, the carb spits the fuel out of the overflow for about 5 seconds then it stops. This cycle is repeated over. I would have normally expected a constant stream.

Any ideas?

Cheers,
Ian

[warren3200gt]

That's carb 3. Carb one is one left as you sit on the bike.
The overflow is flowing more fuel out than the float needles is letting in so it's dumping fuel then refilling then dumping.
The float are likely sticking due to a crungy pivot hinge.
Whacking the bowl with s screw driver handle will usually jar the float back into action.

With the engine running it'll be using the fuel probably keeping the fuel level below the overflow pipe.

[Ultim8pc]

As has been said, sticking float or valve. You'll need to get the bowl off (carbs out to check). Could be debris.

[ian_2020]

Thanks for the replies, I'm sure the problem is just the float or valve sticking and would easily be sorted with some carb cleaner etc.

What I was curious about, and still am, is what is the mechanism for the "fill and drain" sequence that is happening. I would have expected a continuous stream of petrol from the overflow pipe, if the float was stuck down.

By the way, this situation is happening with the engine NOT running.

I'm sure I'll work it out when I strip the carb, but I'm going on holiday tomorrow and don't want this bugging me for two weeks!

[warren3200gt]

The bowl fills to higher than the overflow pipe and continues to do so until the surface tension over the overflow tube is broken. It'll then drain until the fuel level is level with the top of the tube.
It'll continue to repeat each time the surface tension is broken so shows as bursts of flow rather than continual flow.

[ian_2020]

Perfect, thanks!