Petcock problem, will not prime

I have a problem with the vacuum petcock on a kz550 LTD. A month ago the crank case flooded with gas, I figured it was the petcock and rebuilt it.

When the petcock is installed with the vacuum and gas lines attached to the carbs I cannot get the lines to prime. When the knob is turned to prime nothing happens. When you turn it to ON and crank the engine, eventually a little fuel will be drawn through, but not enough to run.

In order to re-rebuild the petcock I drained the fuel tank with another length of tube, vacuum line detached, and the prime setting worked fine for emptying the tank.

I took the petcock apart, made sure it was assembled properly (noticing that the vacuum line plate with 4 screws will fit in a few orientations), and put it all back together. Same problem. Prime won't work. I killed the battery trying to suck fuel down the line. The prime setting appears to work as a standalone tank setting for draining, but something is preventing the petcock from working as needed while all the lines are attached to the bike.

The fuel line has a filter installed with hose clamps just behind the petcock. There is an inch of tube between the petcock and filter before the longer tube turns down to the carbs. The fuel does not have a straight drop from the petcock, but if I recall correctly, it has always functioned the same no matter where the filter was installed. The fuel simply won't flow.

It seems like an easy problem but it has me beat right now. Any suggestions?

Possible clogged in-line fuel filter ??

Good Luck!

"A month ago the crank case flooded with gas, I figured it was the petcock and rebuilt it."

Holly crap... I believe this unfortunately happened but I don't understand how (me old & stupid)...

Even with a bad petcock, how the hell did this go through the crabs & head to back fill into the cases?

Are you sure there isn't something else?

Damn, I'd sure like to hear more about this for understanding how this occurs... Anyone, explanation please for knowledge for me...

OMR

Old Man Rock wrote:

"A month ago the crank case flooded with gas, I figured it was the petcock and rebuilt it." Holly crap... I believe this unfortunately happened but I don't understand how (me old & stupid)... Even with a bad petcock, how the hell did this go through the crabs & head to back fill into the cases? Are you sure there isn't something else? Damn, I'd sure like to hear more about this for understanding how this occurs... Anyone, explanation please for knowledge for me... OMR

Here's an excerpt from earlier thread ---

Sounds like the petcock is still mal-functioning AND float needles are leaking AND the overflow circuits are clogged. Also, maybe a float is sticking or leaking, and perhaps the float levels are set too high. Such problems could exist in one or more of the carbs.

PRI is same as having a direct line from tank without any petcock.

Here's a simplified version of what happens as the fuel flows from the tank into the carb.

Fuel flows into carb float bowl through an orifice in the float needle seat.

Float rises pressing pointed tip of float needle against seat orifice (supposed to completely seal the seat orifice upon float attaining correct height via buoyancy in the fuel). A leak at the needle/seat orifice -- a "leaking float needle" -- due to crud, grit, worn or damaged needle tip or seat orifice, or whatever reason, allows fuel to keep on entering the float bowl.

When excess fuel enters the float bowl past a leaking float needle, the excess fuel goes somewhere -- usually through an overflow system designed into the float bowl, which excess fuel drips to the outside. If the overflow system is clogged, the excess fuel may rise upward into the carb and flow both ways -- forward toward the engine, and backward toward the air filter.

Excess fuel which has not escaped through the overflow and has consequently risen up inside the carb -- flowing forward toward the engine -- gets past the intake valve into the combustion chamber and flows down around the pistons into the crankcase.

Excess fuel which has not escaped through the overflow and has consequently risen up inside the carb -- flowing backward toward the air filter -- either drips from a pod type air filter, or collects inside an air box.

Excess fuel which has not escaped through the overflow and has consequently risen up inside the carb and flowed backward into an airbox, escapes from the airbox either to the outside through the air box drain hole or by draining into the crankcase through the crankcase breather hose.

When the fuel delivery system is working correctly as designed (needle not leaking), there should be no excess fuel being allowed into the float bowl regardless of the petcock position. And any excess fuel which might be allowed through a leaking needle is supposed to escape through the overflow.

When the engine isn't running, turning a properly functioning manual petcock to the OFF position, or leaving a properly functioning vacuum petcock in the ON or RES position, stops fuel flow into the carbs so there is no "excess" fuel to escape.

Caveat - a serious float leak coupled with a faulty floatbowl circuit, may allow excess fuel to enter the crankcase while the engine is running, and of course while riding the motorcycle.

A frequent oil sniff-test is recommended, along with assuring: absence of float needle leakage from whatever reason; correct float height setting; properly operating floatbowl overflow circuit (including clear drip tubes); properly functioning petcock; and always using an in-line fuel filter.

Judging by the condition of my #1 plug the gas went through that cylinder/carb. Two minutes of running on the gas left in the float bowls was enough to clean the plug off. What I have now is almost certainly a fuel delivery problem because I'm using clear fuel line and it's plain to see no fuel is draining.

What I can't understand is why the prime setting works while draining the tank into a bucket, with the vaccum detached, but it won't prime the line with everything connected on the bike. All I can think of is the orientation of my diaphragm cover is wrong. It will fit multiple ways but I have it together just as the manual shows.

Grebnaws Inc. wrote:

... What I can't understand is why the prime setting works while draining the tank into a bucket, with the vaccum detached, but it won't prime the line with everything connected on the bike. All I can think of is the orientation of my diaphragm cover is wrong. It will fit multiple ways but I have it together just as the manual shows.

Not logical that fuel flows from petcock into bucket when set on PRI, but won't flow when attached to fuel line on bike with vacuum hose also attached.

Have already suggested possibility of clogged in-line filter blocking flow through bike's fuel line -- has this yet been investigated?

If the in-line filter is clear (or removed for testing), another possibility could be a kinked or obstructed fuel line.

Perhaps the manual is mis-leading. And some manuals have been known to contain erroneous information.

But am suspicious here that the petcock has been incorrectly re-assembled.

My understanding is that with engine off (no vacuum), an internal spring and o-ring block fuel flow in ON and RES positions.

When functioning correctly, vacuum from running engine sucks the diaphram to overcome the spring pressure so the o-ring no longer blocks flow.

In PRI position, the spring and o-ring don't block the flow, so fuel flows through petcock regardless of whether the engine is running or not running.

Would assure the spring and o-ring are also in good condition.

Good Luck!

On prime the petcock is purely mechanical. Holes in the lever line with holes in the petcock to allow fuel to flow. The diaphram has no effect on prime. So if no gas flows in prime, there's either no air vent to the tank, like a plugged fuel cap vent, the petcock is blocked or somehow assembled wrong.

The filter and fuel line are clear, they are not blocked. The petcock valve gasket (with the 4 holes) is lined up properly, the spring is in the correct position (on the outlet side of the diaphragm)

I know it isn't logical, that's why I'm still scratching my head. I still wonder if the book is wrong. I don't have the bike on premises and would try rearranging the diaphragm assembly again if it were here.

Questions, please -- When draining the tank via the petcock into a bucket,

(a) Was the vacuum line from carb attached to the petcock?

(b) Was the petcock in PRI position?


Here for purposes of comparison is a diagram of the petcock from kawasaki.com (which matches the diagram shown in the FSM covering 77-79 KZ1000).

Good Luck!

[Click on image for larger view]

A. The vacuum line was not attached to the petcock while draining into the can.

B. Petcock was in Prime for draining.

The manual shows a slightly different than the petcock (parts are the same, shapes are different) but it has been assembled identically.

Is there any way that the filter or angle of tube is restricting the flow? Maybe it's airlocked?

Could test for fuel flow through petcock as follows:

Fully assemble the bike (with normal fuel line configuration);

Assure ample fuel in tank;

Leave the fuel tank cap wide open (do not snap it closed);

Turn petcock to PRI position;

Hold a dry rag in place to catch escaping fuel;

Pull fuel line off petcock (so petcock fuel outlet nipple is exposed to open air).

Fuel should flow from petcock (and make a nice mess), if as reported, fuel would under these conditions flow into the bucket.

With ample fuel in tank and cap wide open -- If fuel doesn't flow from the petcock on PRI with nothing connected to the petcock fuel outlet nipple, fuel is obviously not flowing through the petcock on PRI as currently assembled.

Good Luck!