Fuel Leak

1981 KZ1000 CSR M1

I hope I can properly describe my problem, so here it goes. I noticed that when I top my fuel tank off, after the bike sits for awhile, I get a large pool of gas underneath my bike. I say when the tank is down to about half-full, the leak stops.

The previous owner said the fuel petcock did not work properly, so he added his own shut-off valve. He added a lawn mower shut off valve on the fuel line between the fuel petcock and where it goes into the carbs.

I took the gas tank off trying to locate the source of the leak. While doing this, I noticed the fuel was pooling in the air cleaner box. I reached into the carb intakes from the cleaner box and could feel fuel.

So, is my leak coming from the carburators or something to do with the added on lawn mower shut-off valve?

Thank you

Carburator float valve.

Float could be set too high or, most likely, the valve is leaking when tank is full due to head pressure. When the pressure is reduced by less fuel in tank the valve may shut off.
The float needle has a small spring that may get gummed up or weakened and not place sufficient pressure on the needle to control the flow at the higher head.
I have had this problem.

Steve - Your bike year/model added to your signature would make any provided advice a lot more specific...

The way a float works is that it is bouyant and rides on the top of the gas in the bowl. It has a needle that rides in a seat and when the bowl fills, the needle is pushed up into the top of the seat and shuts off the hole that gas comes through.

When the valve doesn't work as it should and gas continues to flow, it will first overflow through tubes located in the bowl on VM models. BS/CVK models don't have this tube and gas just continues to rise till it eventually fills the bowl area totally and comes out the needle jet located in the bottom of the venturi area (the thing your jet needle goes into).

If the overflow tube on VM carbs is overwhelmed, these carbs will also eventually overflow out the needle jet.

When you have gas flowing out the needle jet it can ONLY go two places. 1. AIRBOX 2. COMBUSTION CHAMBER

After you fix the problem, DO CHANGE THE OIL!!! The oil is fouled with gas and dry out your air filter so you are not a fire hazard....

The MOST COMMON cause of flooding is that OLD bikes (like yours may be) rust in the tank. The rust and other sediment makes its way through the gas hose and into the carbs where it is drawn into the float seat. The debris gets between the needle and seat and BINGO... you are flooded. To check/fix:
1. Drain tank, remove petcock and clean screen. Flush tank if necessary or if rusted, line the tank (POR15 or KREEM) or boil it with phosphoric acid. Watch as this stuff eats paint.
2. Start using inline gas filter(s)
3. Open up carbs, remove seats and clean debris. If using BS style carbs, clean screen.

The other common causes of overflow are leaving your gas on when parked. The use of an inline fuel shut off indicates problems in this area. BTW: The lawnmower filter is NOT allowing sufficient gas though for top performance, no matter what model you have. Get a Pingel inline fuel cut off valve if you need this. If you have a gravity petcock, it will say Res/On/Off. If you have vacuum, it will say On/Res/Prime. A gravity petcock must be shut off when bike isn't operating. A vacuum is supposed to shut off. If yours is vacuum and may not shut off, test by pulling off gas hose while bike is off and petcock is in "ON" position. If it dribbles, the petcock diaphragm is bad OR you have a leaking vacuum hose which goes between carbs and petcock.

hwms covered all the other possible causes of leaking... CHANGE YOUR OIL BEFORE RUNNING THE BIKE AS IT HAS BEEN DILUTED WITH GAS!!!

Thanks for the information. Step 1 is complete...I removed the carbs last night(is it me or are those carbs hard to remove?)

Would I need to seperate the 4 carbs before cleaning them? What would be the best method to clean the "seats"? Blast it with carb cleaner and a brush?

Thanks again

The difficulty removing the carburetors likely was caused by old rubber intake manifolds and rubber airbox connectors. It is likely a good idea to replace both sets of these bits as they are potentially cracked and the rubber no longer pliable. A bad seal or crack in the intake manifolds can cause engine damage.

Remove the floats and mark them as to which carburetor they came out of. Replace the needles and remove the seats with a 10mm socket and clean them with brasso and a q-tip. Blow carb cleaner through the fuel inlet(s) and then compressed and reassemble. You may also want to check the service fuel level which is a measurement of the volume of fuel (its level) within the carb bowl.

Well, I got her all done this weekend. I took the float bowls off and found about 1/8' of rust sediment in the bottom of every float bowl. I took the float needles out and cleaned them. Also, each float needle screen was covered in the rust sediment.

I checked my tank and found that it was completely covered with a fine surface rust. I used KREEM and cleaned and coated the tank.

I put it all back together today and started it up. Now, keep in mind it is 30 degrees outside and snowing. The bike starts just fine on full choke, but does not seem to improve after a short time. If I turn off the choke, it dies. I have heard these bikes do not like the cold. Is the poor running attributed to the cold weather, or did I screw something up. I guess I might have to wait till Wednesday when it is 70 degrees(That's New Mexico weather for ya').

I like to thank everyone for their assistance and input. I learned alot about my bike in the process. Thanks!