The International CBX Owners Association

All of a sudden, my '79 X has started dribbling fuel. It only happens upon cold start-up, after she's sat a few days. If sitting more than 3 days, I always have a difficult time starting. Mine has a vacuum valve between the petcock and the carbs, so it takes a while cranking to get fuel in the carb bowls.

Ordinarily, I would suspect a sticking float. But the bike runs as well as it ever has, and after riding a short time there is no longer fuel dripping from the overflow tube. You think maybe she's just flooded? Any other thoughts on what the problem might be? She's always been hard to start after sitting, but she didn't used to drool.

I'm probably the least qualified to answer but it sure sounds like a float valve is in need of replacement.

If you pulled the overflow tubes you might be able to determine which carb is leaking.
I am thinking along the lines of a cracked stand tube in one of the bowls?

steve murdoch icoa #5322 wrote:If you pulled the overflow tubes you might be able to determine which carb is leaking.
I am thinking along the lines of a cracked stand tube in one of the bowls?

+1

Z, Study it closely to find the rue source of the leak. If it's a stuck float, the fuel should be coming out the overflow hose under the bike. If it appears anywhere around/under the carbs themselves, I'd suspect a withered o-ring at one of the tube connections between carbs. As you mentioned, it quits after a short time; and, then, the bike runs good.The old o-ring is just doing a little swelling after it sits in fuel for a short time. At this point, I'd say your remedy is one of two things: 1) Put a rag under it for a minute or two until it quits leaking and go ride!; or 2) Pull the carbs, separate them and install all new o-rings. (BTDT)

Thanks for the replies. It is definitely leaking via the overflow hose, so I suspect some sort of float issue. It even runs fine while its leaking. The O-rings were replaced about three years ago when the carbs were completely rebuilt by Tim's. I'll pull the individual hoses and see if I can pinpoint the offending carb. At this point, I'll probably just deal with the leak since I don't have the expertise to work on them. Maybe I'll get lucky and its either 1 or 6 so I could remove the bowl and have a peek at the float.

How long ago was the rebuild done by Tims?

Most likely you have a float needle that's not seating or a stand pipe in the bowl that has a hairline crack in it, do you understand the concept of the cracked stand pipe? It will weep fuel through the drain hose until the bowl goes dry, that is if your float is working properly.

If it's a float problem it will weep constantly unless you have a vacuum petcock.

You're on the right track though, isolate the suspect carb by pulling off the drain tubes and seeing which one is weeping.

The carbs were rebuilt about 3 years ago. Honestly, I have never been inside a carb, so I don't know exactly what the stand pipe is or does. I couldn't find it referenced in the factory service manual.

Z Grand wrote:The carbs were rebuilt about 3 years ago. Honestly, I have never been inside a carb, so I don't know exactly what the stand pipe is or does. I couldn't find it referenced in the factory service manual.

There is a stand pipe in each carb bowl, it rises up straight from the bottom of the bowl towards the bottom of the carb body, it is hollow from top to bottom, it is seated in the bottom of the bowl but has a passage to the drain on the outside of the bowl ( where the drain tube is affixed ) when the fuel level exeeds it's operation level inside the bowl it exits through the top of the stand pipe and out the drain tube to the atmosphere to prevent the carb bowl from over filling.

If the float needle, seat and the vacuum shutoff are working properly and the stand pipe has a crack in it or is no longer seated in the bottom of the carb bowl, the fuel will weep through the side of the stand pipe and out the drain tube until the bowl goes dry.

Great explanation - thanks!

Hello Z,

If the carb is dribbling switch off the fuel and wait for it to stop. Then open up the float drain for the dribbler and catch the fuel, do the same to a good carb and compare the amount of fuel. If there is a lot less fuel from the dribbler then it is likely to be a cracked pipe, if the same volume then probably a faulty float valve.

Regards

Goss

Goss:
Idea is good except for one thing - the first bowl you drain will also drain the fuel manifold and piping, or some of it anyway. This will result in a false reading of the amount in the first bowl drained (or the first on each side for the '80-'82). My bet it a weeping float valve.

Dave