Float needle issues, 1980 KZ750 LTD

Hi, I've been having some issues with the Keihin CV34's on my 1980 KZ750 LTD. One of the carbs keeps leaking gas out of the float bowl. The float height is fine, the float isn't damaged, it appears that the float needle keeps sticking open, allowing gas to flow. I've replaced the float needle about 3 times now. Each time it works perfectly, but about 2 months later it begins to leak gas again. Any idea what could be going on/any solutions to fix this ongoing problem? I'm going to take some sandpaper and sand the edges of the float needle down, hopefully that will keep it from sticking for awhile. The float seats on the CV34's are not replaceable. Thanks in advance

Hi astark
I would stay away from using sandpaper. At least for the moment. Do the seats look damaged ?
I have found that using Brasso liquid on a Q tip followed by carb cleaner will clean up a dirty seat and make the seal a whole lot better. If you dont have a fuel filter on the fuel line then i would suggest installing one as the tiniest piece of rust can cause a leaky float valve.
You shouldn't need to replace float needles every couple of months. Are you using any type of fuel additive which could cause the tip (rubber ?) of the float needle go out of shape? I might replace float needles every few years at most.

Are you using OEM float needles? The aftermarket ones are prone to having weak spring structures.
I had problems with my aftermarket ones; went back to OEM and the issues went away.

astark wrote: Hi, I've been having some issues with the Keihin CV34's on my 1980 KZ750 LTD. One of the carbs keeps leaking gas out of the float bowl. The float height is fine, the float isn't damaged, it appears that the float needle keeps sticking open, allowing gas to flow.

In my experience, it's more often caused by a piece of crud keeping the needle from seating well.

Can you visually inspect the surface that the needle tip seats against? If it is dirty or rough, it won't seat tight and will leak. You may be able to polish it using a tool cut from a popsicle stick. Cut it narrow enough and then angle the tip and use some brass polish to turn it by hand and polish the seating face.

If the tip of the needle is all metal, you can put it in a drill and spin it and polish it smooth with 600 grit paper and oil. If the tip is rubber, just clean it with solvent.

Note: I started using Lucas fuel conditioner and it keeps the carb cleaner because it prevents gas from oxidizing into sticky slime. Might help if you have chronic problems.

Thanks for all the advice. I took a look at it today, and found that the seat looks like it has a rough spot where the needle sits. I'll try and get a better look at it tomorrow, but if the brass is damaged is there anyway to fix it? Will polishing it work?

I used a small drill bit BY HAND spinning it reverse direction to VERY LIGHTLY polish the seat, then polished more with the popsicle stick trick I mentioned above with some chrome polish.

Is the seat not removable?

If not, be very careful with it.

My keys were stolen, hindering me from working on the carbs, but after drilling out the seat lock and replacing the ignition lock, I replaced the float needle. This time it still leaks. I'm going to have my mechanic friend take a look at it, but I have no idea what it could be. The float bowl O-ring looks good, the float height is good, the float isn't damaged, there's a brand new float needle in it, and i gave the carb a thorough cleaning. The only thing I can think of is that the seat is damaged, however the seats can't be removed. I'm going to see what my friend has to say, but I think I might have to replace the whole carb. Thanks for all the help.

Bummer about your keys being stolen

Are you sure the float and needle are at fault ? The brass overflow tube in float bowl could have a crack in it - it happens. Happened to me. To check, take the bowl off, put a rubber tube on the overflow nipple, fill bowl with water, put finger over the open end of the brass tube and blow into the rubber tube. Watch for bubbles to pinpoint a leak..

If this is the problem then its an easy fix
JB Weld as long as its allowed to cure properly. or get a slightly wider brass tube from a hobby shop and slip it over the existing brass and solder the bottom.

Check also the drain screw and o ring

Good luck

You say "the float height is good" and I'm sure you're correct. However I've got a different theory about alcohol and plastic floats. I believe that the plastic absorbs alcohol from the doo gooder fuel we have in this country as a result setting the height of the float dry might just mean nothing. Are your floats plastic foam? If so i suggest that you check the fuel level with a clear tube to see where the fuel level really is.
I fought the same problem as you for a couple of years till I relented and went the clear tube method. What I found was that I had to bend the tang pretty radically till the fuel level would stay 5.5 to 8.5mm below the bowl gasket as the manual specified. This was on my 1300 but you could be having the same problem.

Bill

astark wrote: , the float height is good,

Checked with clear tube?

You said before there is a rough spot on the seat the needle tip mates with. If so, it will always leak.

So, here's a thought. What about using valve lapping compound? You know, the kind we use on our engine heads?

koolaid_kid wrote: Are you using OEM float needles? The aftermarket ones are prone to having weak spring structures.
I had problems with my aftermarket ones; went back to OEM and the issues went away.

+1 :ohmy: