Leaking Float Bowl

OK Guys I have a drip coming out of the nipple of the carb bowl on the #2 cylinder. The Bike is a 1981 KZ750 4 Cylinder LTD H2. I installed a rebuild kit from Z1 Enterprises a copuple of weeks ago so the float needle is new. I thought it might have been a bad float bowl so I replaced it with a spare. The leak is definately coming out of the drain only and nowhere else. I put a plug over the nipple on the float bowl and it has not leaked at all. When I had the float bowl off. I removed the float and cleaned the float needle seat but still no luck. Any Suggestions?

Are these Keihin CV34? The drain screws on those carbs are made of steel and rust. They tend to actually shorten and not seat all that well. I have had some drip in the exact way you describe even with a new oring. Swap drain screws and if the problem moves you will know what is causing it.

I replaced the old screw with another old screw and it still has a very slow drip. When I had the float bowl off of the Carb I filled the bowl with carb cleaner and let it sit for a while (Approx 5 mins.) and it did not drip. but when I put it back on the carb and turned on the fuel, it dripped so I put a cap over the nipple to see if gas is backing up into the carb and it dosen't appear to be. 2 different carb bowls on the same carb with the same problem What else can I do? Float adjustment?

i think the drip may be coming from elsewhere on the carb, possibly the gasket itself is leaking or even the fuel line going between the carb bodies.
Mine is doing the same thing but i am too lazy to take the carbs off again for the 5th time in three weeks to repair it.
Mine will leak badly when i use the kickstand, nothing happens while on the center stand.

I wonder if the bowl has a crack that opens up when the bowl screws are tightened, but when it's off the carb the crack is leakproof??? Jus' wondering...

Just some random and rambling thoughts here
What is the fuel service level like ? Put a clear tube on the overflow nipple and hold it up alongside the carb body. Open the drain screw and the level in the tube should come up to about a couple of mm below the joint between the bowl and the upper carb body.

There's a brass overflow tube that rises straight up from the bottom of the bowl. I had one of these with a hairline crack in it and the carb would drip slowly from the overflow nipple. Found it by filling the bowl with water and with a rubber tube connected to the nipple and a finger over the open brass end , blowing in the rubber tube....sort of like looking for puncture in a tire under water. I did a temporary fix with JB weld and later a more permanent fix using some slightly larger diameter brass tubing froma hobby shop and slipping it over the existing brass tube and soldering in place at the bottom.

Just noticing your second post where you say you had same problems with two different bowls on the same carb so that would tend to rule that idea out.

Perhaps swap 1 and 2 carb bowls and see if the problem follows the bowl or if it stays with the carb in which case maybe look again at the float needle and seat.

Perhaps the float needle seat orifice is not yet perfectly clean and smooth, so that the float needle tip isn't completely sealing against the orifice. Have heard of using a q-tip to twist inside the seat, maybe even with the q-tip as a "bit" in a drill on slow speed. But am uncertain whether the q-tip method has already been done or would even be feasible with these particular carbs.

With #2 carb bowl removed, and fuel being allowed to flow into the carbs, is it possible to stop the leakage through the float needle/seat interface by using very light finger pressure to hold the float up so the tang presses against the float needle (using finger pressure in lieu of fuel buoyancy)? If leak continues, more suspicion is cast toward failure of the interface. If leak stops, it's remotely possible that the float is set too high for the tang to press the needle against the seat, but probably more likely that finger pressure is enough to seal but buoyancy pressure isn't.

Just thoughts.

Good Luck!

Do you know what causes gasoline to drip out of the over flow drain tube of your carburetor?

The short answer is that a tiny piece of dirt is, most likely, stuck in the needle and seat of the float valve, preventing the valve from fully seating. Or else your float valve may need to re-adjusted to obtain a correct fuel level in your carburetor's float bowl. Or if your if your carburetor's needle valve and seat are excessively worn, they may start leaking and need to be replaced.

However, I'd like to give you a bit more background on this important question. I used to think that the float valve in the carburetor operated like the float valve in the tank of a toilet: i.e., when water in the tank got low (as in after flushing), the valve would open until the tank filled and then close again. However, it is important to realize that (unlike our toilet tanks) the needle in the carburetor float valve is always closed, while the fuel level in the float bowl is being maintained. What varies is the pressure that the carburetor float exerts on the needle: relatively high as the fuel level increases, and relatively low as the fuel level decreases.

This means that the fuel pressure (on the inlet side of the valve) is working in constant equilibrium, as it's equalizing with the pressure exerted by the float valve needle (on the carburetor side of the valve), so that a very constant level is maintained in the float chamber.

Understanding that the needle of the float valve is always being pressed against the seat is important in understanding why any tiny bit of dirt can cause so much trouble. Once a piece of dirt gets caught between the needle and the seat, it will be held there and interfere with the needle valve's ability to control the fuel level, until such time as fuel is drained from the carburetor and the piece of dirt is flushed away. This is the reason for the flushing procedure of the fuel system, by removing the drain plug from the bottom of the float bowl and let enough fuel run out. Which will usually rinse off the the debris that is on the needle valve and seat, providing the debris is small enough to go through the needle valve seat orifice, as the fuel is draining out of the float bowl drain screw hole.

To help prevent this problem from happening, again. It's advisable to put a good reliable inline fuel filter between your gas tank and carburetors to keep your fuel system as clean as possible that's going to your carburetor's float valve and seat. Which will, also, prevent other problems from occurring in your carburetor, too, from dirty fuel.

In addition to dirt causing the valves to stick open, I have seen a few cases where the brass seat of the float valve needs to be polished (smoothed out) by pressing and rotating a short, sharply pointed hardwood dowel into its small orifice. Dowels of 3/16” diameter work well. I have even had to clean up brand new seats in this fashion before they would stop leaking.

Keihin CV34 carbs have float seats that can't be replaced. you need to clean them. A q-tip and some Brasso seems right to me... wash out the seat with carb cleaner when you are done.