Fuel Leak

I have a set of Mikuni 29mm smoothbores and the #1 carb is leaking fuel into the pod. I took the carb off of the bike and there is fuel leaking from the air jet. I checked the fuel level via the clear tube and it is correct. What would cause fuel to leak out of the air jet ? Thanks.

As smoothbores don't have overflow circuits, failure of the float valve (for whatever reason) to regulate incoming fuel allows fuel to rise up into the carb throat. The excess fuel flows rearward toward the pod or stock filter. And the fuel also flows forward where it may enter the cylinder and flow past the pistons on down into the crankcase, diluting the oil.

Would suggest a sniff-test and physical examination of the crankcase oil.

If the oil has been contaminated with gasoline, would disconnect the fuel line from the carb, and change both oil and filter, and not allow any gasoline into the carb until the overflowing problem is corrected.

Good Fortune!

I took the float and the needle under the float out of the leaking #1 carb and moved it to the #2 carb and took the parts from the #2 carb and put them in the #1 car to see which carb would leak. I filled the carb with rubbing alcohol and the #1 carb leaked again. I took the carbs apart again to put the float and needle back where they belonged when I noticed that the copper pipe (starter pipe) has a crack in it. Could that be what is causing the fuel to leak out of the air jet into the pod ? Any help is appreciated.

BIGKEVIN wrote: I took the float and the needle under the float out of the leaking #1 carb and moved it to the #2 carb and took the parts from the #2 carb and put them in the #1 car to see which carb would leak. I filled the carb with rubbing alcohol and the #1 carb leaked again. I took the carbs apart again to put the float and needle back where they belonged when I noticed that the copper pipe (starter pipe) has a crack in it. Could that be what is causing the fuel to leak out of the air jet into the pod ? Any help is appreciated.

I doubt that the cracked starter pipe is relevant to the overflow issue.

First guess would be crud where the float needle fits into the seat.
Might help to polish the seat with a Q-tip chucked into a drill.

Or perhaps the float is leaking.

Question: Did the overflow begin on its own, or after a reassembly of the carbs?

On some carbs -- I don't remember about the 29's -- it's possible to install the float upside down.

Good Fortune!

I didn't do anything to the carb lately. I was cleaning it and noticed the fuel leaking. I did some checking on it today and it looks like either the needle valve assembly or the gasket. Whenever I put the needle valve assembly from the #1 carb would leak. Looks like I'll have to order a needle valve assembly and gasket. I did try cleaning it the valve assembly but it still leaked. Thanks for the information Patton.