All carburetors overflow. After all, the mechanism that ostensibly prevents it is nothing more than a miniature toilet valve, and not even as sophisticated. There are too many things that can either override this valve or cause overflow even when the float valve is working perfectly. Overflow and leaks will happen, count on it.

Here then are sixteen reasons why your CBX1000 carbs may drip fuel. There could possibly be more.

  1. Cracked overflow tubes

By far the most common reason for overflow on the CBX. Two repairs are available. First, 90 percent of the cracked overflow tubes can be repaired by soldering. The other repair and the one I use when the crack is either too wide or it reaches to the bottom of the float bowl, is to simply replace the tube. There are even pre-made ones available on the aftermarket now.

  2. Worn or Chinese float valves

Old float valves that have many years on them can be worn or the rubber tips hardened or distorted. Chinese float valves, meaning all of those not OEM, come already working poorly.

  3. Dirty float valve needle

A dirty float valve needle has fuel residue or other contaminants stuck to it. It may even be corroded.

  4. Dirty float valve seat

Just like the float valve needle, its mating part the seat can be dirty, and often is more than the needle.

  5. Burnished float valve seat

This is when someone puts abrasive onto the float valve seat. Don't do that. It changes the shape of the seat's sealing surface.

  6. Obstructed float bowl vent

The float bowl vents on the CBX carburetor are between carbs #2 and #3, and between carbs #4 and #5. It they are blocked either intentionally or unintentionally, fuel will gush out of the carburetor bore due to the air lock created in the float bowls.

  7. A bad float bowl drain screw

The CBX carburetor drain screw has a taper that is subject to rusting badly when water sits inside the carburetors.

  8. Old, shrunken passage o-rings

There are 31 o-rings sealing up the passages on the CBX carb set. The original from the factory are pretty good quality. After all, they have been observed to last more than 40 years. But time will get to them, making them shrink and harden.

  9. A cracked fuel feed tee

The CBX fuel feed tee is silver-soldered together. It shows up every now and then a leaker, almost always due to rough handling.

10. Cracked connecting tubes

The aluminum interconnecting tubes are very minimalistic, thin-walled, light weight. Inexpert disassembly or assembly can fracture them easily. The ones most at risk are the two curved center ones.

11. Leaking float bowl gaskets

This one is obvious but often overlooked, and is especially a problem when the crappy gaskets that come in carb rebuild kits are used.

12. Leaking float valve

In other words, a float valve that won't shut all the way off. The float could be distorted and thus rubbing on the inside of the float bowl.

13. Incorrectly-sized or poorly attached fuel hose

Many times a fuel drip that appears to be coming from the carbs is actually coming from the fuel hose where it attaches to either the tank or to the carbs' fuel tee. Here's a tip. If you need anything more aggressive than the OEM fuel clamp to make your hose fit tightly, the hose is too big.

14. Leaking fuel valve (petcock)

Similar to the issue immediately above, fuel can run down from the petcock and down the hose and when dripping from the carburetor look like a carb drip. The CBX petcocks are rebuildable, but they are also readily available as new replacements.

15. Excessive crankcase pressure

Since the air filter box is connected to the engine crankcase, excessive pressure resulting from cylinder blowby (common on a CBX) can find its way into the float bowls. This will push fuel back out of the float bowls as it enters.

16. Too high a float level

This is listed last for a reason. It is very rare. Yes, it is possible to get the float level so far off that fuel rises above the height of the overflow standpipe. But in that case, fuel will enter the carburetor bore at more than double the normal richness, resulting in such poor running that you will be more concerned with that than with fuel escaping.