TOPIC:

Hi everybody. I have a 76 KZ400 and every time I fill the gas tank to full, the fuel runs out of the carb overflow tube. What is wrong with this thing... I think the petcock is bad too, because even if I try and shut off the petcock it still drains the tank. This is a rotten problem because the bike will be fine, and a hour or two later the garage floor will be covered in gasoline. Is it a carb float?

I'm not familiar with the 400/440s, but on the 650s, the fuel petcock will not flow when in the ON position with the Vacuum type of petcock (while the engine is not running) or with the Non-Vacuum type, the fuel will not flow with the petcock in the OFF position.

Also the float should raise and close the Float valve (or whatever it's called) to close and stop the flow of fuel.

Sounds like you may have a problem with both your fuel petcock and float valve in that carb.

you need to replace the needle and seats in the carbs, and see if a kit is aval for the petcock, benn there done that

Likely the float itself is just fine and needs no adjustment.

Fuel flows from the petcock into the carb through a small hole in the float needle seat and from there on into the float bowl. The fuel level inside the float bowl is regulated by the float which has a tab (an adjustable tab) that presses up against the float needle as the float rises and pushes the needle into the seat thereby closing the hole and stopping the flow of fuel into the bowl as the fuel level reaches the correct level.

A tiny sometimes imperceptible piece of grit or crud between the needle and the seat may prevent the needle from closing off the hole in the seat which then allows fuel to keep on running into the bowl and consequently overflow through the overflow nipples from bottom of the bowl. (A worn out tip on the float needle has the same result due to its inability and failure to close the hole in the seat).

Often, a good cleaning of the needle and seat will cure the problem. Remember each needle is matched to its particular seat, so do not mix and match. (This is why both needle and seat, when replacement is necessary, should be replaced together as a matched pair).

The overflow may be coming from one or more float bowls. And exactly which float bowls are leaking should be first determined so you'll know which carb needs attention to the float needle-seat area.

If there's crud in the float needle-seat area, it's likely other places inside the carb as well. Which suggests need for a complete cleaning of all the carbs (and beyond the topic of this thread).

While a properly operating petcock will stop fuel flow into the carbs, it does not cure the carb problem. Sometimes a petcock repair kit works -- sometimes not.

At the least, install a new in-line fuel filter, and it might help to cross your fingers and add some "carb cleaner" additive to the fuel in the tank.

Good luck.

Patton,
Thanks for the in depth reply. I will see what I can do.

Patton wrote:

Likely the float itself is just fine and needs no adjustment.... Remember each needle is matched to its particular seat, so do not mix and match. (This is why both needle and seat, when replacement is necessary, should be replaced together as a matched pair)....

Boy,,, did I learn _that_ one, replacing needle _AND_ seat as a set that is, the hard way.

Depends on the carb. The float needle seats on my Keihins are not removable. I can only replace the needles themselves.

JR wrote:

Depends on the carb. The float needle seats on my Keihins are not removable. I can only replace the needles themselves.

Believe JR is absolutely right about Keihin float needle seats being not removable. Believe Keihin seats are pressed into the carb body (not screwed in like Mikuni). Always thinking Mikuni:blush:.

If float needle has a pointed rubber tip, check it carefully for any imperfection that would impair its precise fitment in the seat.

I should have expanded in my post. I think the 400s have Keihins and I did'nt want speedadict trying to prise out the seats. I made that mistake once but luckily I failed and the seats survived

Had the same problem. Connected hoses on the overflow tubes going to individual containers to see which carbs are leaking. I also removed the fuel hose from the tank and connected a hose to a container just to see if my petcock was ok.All carbs and petcock was leaking.Solved the problem by cleaning the carbs and replaced the petcock.Didnt install a fuel filter coz the petcock had a built in one.

jeffreygp wrote:

...replaced the petcock.Didnt install a fuel filter coz the petcock had a built in one.

The OEM non-vacuum petcocks came with a small removeable screen filter in place above the sediment cup, and with screens on the fuel pickup tubes inside the tank. Believe the vacuum style petcocks came with larger screening on the intakes without the sediment cup arrangement. Would guess either style works okay for a while. But IMO accessory inline filters should also be used because they are cheap, allegedly more efficient than petcock screens, and easy to install.

Have no proof of inline filters being more efficient than the petcock screens, just an understanding.

I gotta agree with Patton here... and I think most others would agree also that those petcock screens are not really much good and an inline filter is practically a "must have".

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