1981 kz650 CSR has leaking petcock

My 1981 Kz650-H1 'CSR' has a vacuum-actuated petcock.

SYMPTOM: with the bike sitting, gas flows out of the carb overflow tubes. Gas also flowed into the bottom of the airbox -- apparently the fuel level got so high in at least one of the carbs, it reached the rubber airbox-to-carb boot and spilled over into the bottom of the stock airbox.

Looks like something has failed on the petcock.

This is like most vacuum-activated petcocks from those days -- it has 3 positions:
- prime, which fills the carbs, say, after a carb removal/cleaning
- On
- Reserve

Engine vacuum (routed by a rubber hose from one of the carbs) pulls open a diaphragm inside the petcock and allows gas to flow out of the tank only when the motor is running.

When the motor is not running, there's no vacuum and the diaphragm is supposed to close back up and prevent gas from flowing out of the tank.

I completely disassembled the petcock, looking for anything obvious. Re-assembled. Gas is still dripping out of the petcock in the 'On' and 'Res' settings. I did notice the round rubber gasket with 4 holes in it just behind the petcock knob looks pretty worn.

QUESTION: Will a 'petcock rebuild' kit fix this, ie. do those rebuild kits always fix work-out innards that cause leaking?

Would attempt rehab via Z1E kit.

Would also sniff-test crankcase oil and examine its physical characteristics to determine whether gasoline has entered the crankcase.

From the symptoms described, would suspect one or more of the carb overflow circuits has failed. Could be blockage anywhere from entrance to intake tube inside float bowl to exit from hose underneath the bike.

Good Fortune!

Patton wrote:

Would attempt rehab via Z1E kit.

Would also sniff-test crankcase oil and examine its physical characteristics to determine whether gasoline has entered the crankcase.

From the symptoms described, would suspect one or more of the carb overflow circuits has failed. Could be blockage anywhere from entrance to intake tube inside float bowl to exit from hose underneath the bike.

Good Fortune!

Wow, subtle. Either I subconsciously convinced myself the flow rate of gas into each carb overcame the flow rate of the carb's overflow or got too fixated on the problem in front of me, the leaking petcock, and it never occurred to me, or just too much beer brain damage, I'll go with 2 and 3 here. :S

I have to take the carbs off again, you're right. One of the overflows must be clogged.

I've got to toughen myself up and just 100% disregard anything a prior owner says. He said "I pulled and completely cleaned the carbs, you don't need to do anything there." Meanwhile at least one overflow is apparently clogged, and I'm dropping 1, sometimes 2 cylinders when the throttle's using the Pilot circuit, which means the carbs need to be disassembled and cleaned completely, the right answer is when a seller tells me anything I will just 180 that, what the hell.

Thanks for pointing that out, gives me another reason to pull and clean them.

-

While oyu have the carbs off, do a good proper cleaning, making sure that all circuits in the carbs are clean and cleaner can squirt through. The float valves should be able to stop fuel permanently. THEY SHOULD NOT LEAK at all. I can leave the fuel on for weeks on my bike, and there is never a drop that gets past properly setup floats.

All this gas going up and down in the carb bowls effects performance too... think how the carb is easily overflowing while at an idle... trust me it is happening.

REPLACE THE OIL, there is gas in there even if you cant smell it!

An ounce of prevention...

Good luck!

TeK9iNe wrote:

While oyu have the carbs off, do a good proper cleaning, making sure that all circuits in the carbs are clean and cleaner can squirt through. The float valves should be able to stop fuel permanently. THEY SHOULD NOT LEAK at all. I can leave the fuel on for weeks on my bike, and there is never a drop that gets past properly setup floats.

All this gas going up and down in the carb bowls effects performance too... think how the carb is easily overflowing while at an idle... trust me it is happening.

REPLACE THE OIL, there is gas in there even if you cant smell it!

An ounce of prevention...

Good luck!

Here's my poor memory kicking in, is the risk of gas in the crankcase limited to one risk that being 'unplanned ignition' ie. 650-engine-becomes-bomb when the engine's been running for awhile and gotten really hot?


And I thought about the 'check valve' effect of the float valve. Maybe I need to check/replace the float needle and seat as well?


Martin thanks for the heads up about the cross reference to the police bike, I am still trying to figure out my game plan here, petcock rebuild kit vs. new petcock, maybe rebuild kit for carbs, new oil filter? lots of stuff to decide on here.

Regarding fuel intrusion into crankcase - - -

Say, for whatever reason, excess fuel is getting past the float valve.
Fuel level rises inside the float bowl.
Fuel reaches overflow level, where overflow circuit is supposed to allow fuel to escape before rising higher.

Say also, overflow circuit is clogged, for whatever reason (anywhere from tube entrance inside float bowl through exit from hose underneath bike), or carb doesn't have an overflow circuit.
Fuel level keeps rising, beyond overflow level, and on up into the carb throat.
This can happen with the bike parked or while riding. Thus, a perfectly functioning petcock is desirable, but isn't a panacea.

Fuel rising up into the carb throat flows both ways, back toward air box or pods, and forward toward the engine.
Fuel flowing back toward the air box or pods, can drip out of the pods or go into the air box.
Some air box designs allow an escape route for the incoming fuel.
Other air box designs permit the incoming fuel to flow through the crankcase breather tube into the crankcase. This is why some folks prefer to route a different crankcase breather hose to underneath the bike.

Fuel in the carb throat flowing forward toward the engine proceeds through the intake ports/valve into the combustion chamber, and flushes down around the piston into the crankcase.

Sometimes, fuel intrusion into the crankcase will be evidenced by an otherwise unexplained increase in the indicated oil level. For example, the sight glass may appear "full."

Good Fortune!

Okay the petcock rebuild kit came in today -- it has all the petcock wearables: rubber diaphragm, o-ring between tank and petcock; o-ring around the circumference of the on/res/pri lever; the round rubber 4-hole trip that sets inside between the lever and the petcock body;


BUT NO DIAPHRAGM SPRING!

Sh_t I think that is the most important part here!

This spring pushes on the diaphragm to keep it shut when the motor's off so no gas flows, but it is made of light enough spring-steel to allow engine vacuum to overcome this spring and open the diaphragm.

So since my petcock was leaking (hence the purchase of the rebuild kit) then there is a *fair* chance that this spring got wore out and wasn't pushing the diaphragm shut far enough when the motor's off.


And yet there is no new spring in the petcock rebuild kit. Wow man disappointed.

I could go to the hardware store and get a correctly-sized spring but if the spring is make of the wrong gauge of spring-steel (too heavy) then the diaphram will never open.


You would think they would include ALL the petcock parts.

Take a look at Kawasaki.com. I believe you will find the spring you need is part number 92081-1240. This is still an active part and according to RonAyers.com cost $1.72. If I were you I would get one and put it in while the petcock is apart just to eliminate it as a possible cause. Ed

650ed wrote:

Take a look at Kawasaki.com. I believe you will find the spring you need is part number 92081-1240. This is still an active part and according to RonAyers.com cost $1.72. If I were you I would get one and put it in while the petcock is apart just to eliminate it as a possible cause. Ed

Hot diggity dang thanks Ed I will do just that. It will save the disappointment of putting in all new petcock parts but still having a leak.