TOPIC:

This is odd. I have a vacuum petcock on my '78 KZ650. There have been two incidents where I have run completely out of fuel, even though I have the fuel lever in the ON position. When I flip it to the RES position, there is no fuel left in the tank. I tested the petcock with the tank off the bike, and here is what I found.

PRIME. . .fuel flows without vacuum needed.
ON. . .fuel flows with vacuum applied, until it reaches the reserve point, then it stops flowing.
RESERVE. . .fuel again flows, with vacuum applied, until the tank is out of fuel.

So every thing appears normal, until I start riding.

If I don't refuel within about 3 miles of my indicator light coming on (90 miles or so,) I'm going to have to push a 1/4 ton aggravation *somewhere*. It isn't like there are always fuel stations available within three miles. So I don't want to leave the bike stranded somewhere, and take the gas tank off and start walking towards a fuel oasis. Any ideas? (Besides always fill up before riding)

I've run out twice as well. And each time I should have had some in RES too. I don't have the warning light, but I use my trip meter to let me know when I need to fill up. I've been meaning to check my RES delivery circuit, but it was in 2005 that I ran out twice, and in 2006 I was a little more careful and did not run empty, so I did not check.

What I'm suspecting is happening is that there is a cross over (or whatever) between the RES and ON fuel delivery circuits that's allowing the fuel to keep running past what is normally supposed to cut of and make me switch to RES. So by the time I'm getting fuel starvation symtoms, the tank is already past the RES switching level.

I did some thinking on this issue and remembered "a detail" which might provide some insight here. I noticed that after about 9k miles, I developed a random misfire on the plug which is the second one from the left (while sitting on the bike). The plug was noticeably darker than the other three. . .perhaps fuel fouled? It occurs to me that this is the same cylinder which provides vacuum to the petcock. . .so. . .maybe I have a perforated diaphragm which would explain the loss of mileage and empty tank mysteries. . .

Is there any way to test what I am sure is a very expensive part to replace?

It is not expensive to replace or rebuild a petcock, you can go to www.z1enterprises.com and read the write-up about petcocks. You can replace yours with a manual petcock and have no more problems for about $35.

To answer your question about testing, I think if the #2 plug is fouling, you may have a bad diaphragm in the petcock. A tear or bad seal would allow fuel to suction past it, into the tube and then the #2 intake manifold. You can unhook the tube from the manifold and while still hooked to the petcock apply a vacuum with your mouth. If you get a mouthful of gas I think you found the problem.

Rebuild kits are cheap but most of the time don't work for long. I recommend installing a manual petcock with the correct adapter plate and plug off the vac tube on the manifold. I think 7/32" cap plug is the size.

I rebuilt the original petcock, didn't work. I replaced the petcock with one from ebay, (old & used), didn't work. Then I bought a Drag Specialties petcock w/reserve and adapter plate,works great now.

I've had the same problem on no.2 cylinder, the backfiring, the hissing,flames out the tail pipe...trust me there are flames. and I pulled everything,carbs to the head to see whats going on in there and I thought it was oil on the plug but turned out to be fuel(I have gumout in my fuel and it was cleaning the soot off the head like it was just running in the cylinder). So OKC, what does the petcock have to do with this prob. I found that myfloat valve needle was a little rough on the springy part and didnt return till I cleaned it up, and my accelerator diaphrapm in the carb needed replacing for a long time nowbecause it was sagging and that in turn caused a over delivery of fuel I guess?

I think KaZoo Cruiser figured it out.
Lets say the diaphragm in the petcock is bad, it has a very small pinhole or is not sealing around the edges. It works but just works enough to run.

When the vacuum supplied by #2 manifold pulls opens the diaphragm to let fuel flow into the main line, it is also pulling a little fuel into the vacuum line at the same time. This little bit of extra gas gets dumped in cylinder #2 creating a richer mix, and fouling the plug.

And maybe with a leaky/faulty diaphragm it pulls gas from the reserve port in the petcock all the time. When the low fuel light comes on it is basically empty at this time. It will not matter if the petcock was set to ON, it was stealing gas from the RES setting all along.

Just my rambling, I'm not charging for this


Oh p.s. I use my trip meter to track my fillups too. I have no idea how far Reserve will take me and don't want to find out.

Post edited by: OKC_Kent, at: 2007/01/02 17:06

OK makes sense. so that can also be my problem. Well my head and carbs needed pulling anyways, had to replace chain dampers and seals and gaskets., but now I know whats next!

Well golly. . .mystery still unsolved. . .

I did the vacuum leak-down test on my petcock and found that I don't have a leak. . .no "mouthful of gas," no, not even a bit of anything to take away that hint of minty freshness, so sterner measures are called for, apparently.

I took the silly thing apart and saw TWO diaphragms, one to route the fuel, and the other to receive actual vacuum from the manifold. . .so my random misfire and discolored plug on the vacuum feed cylinder is probably due to age of the plug and coincidence. (The misfire started and unburned fuel discolered the plug, rather than too much fuel soaking it)

I did see on the other side of the petcock that there is a highly machined (ummm, overengineered) rubber seal with four holes in it, one of which had some erosion wear on it, so maybe the fuel was or is leaking from that particular unsealed port. Four o-rings would have been easier and cheaper I am sure, but I digress.

Since I have a way to carry extra fuel on board, I guess I need to carry extra fuel onboard, to see if I did any good by re-orienting my rubber daisy wheel. My guess is that wearparts aren't available unless you buy the entire petcock.

By "wearparts" what do you mean? Rebuild kits are available and don't cost much. The link I posted to Z1 should help. Good luck and I hope no more pushing home.

I ordered that "overengineered, rubber seal with four holes in it" from a Kawi dealer, to repair a leak I had about two years ago, and that solved my problem. My petcock was just dripping at the time if I recall correctly.

Can you describe your leak in more detail Nick? Is it the same problem as Kazoo? I mean that no.2 cylinder flooded with gas

Post edited by: kzwolfsr, at: 2007/01/07 12:39

Hi Ya'll. I am new to this website. I just acquired a 78 KZ1000 from my dad. I too am having problems with the #2 cylinder and gas. Everytime I start it up the drain tube on the second carb. just gushes fuel. Does anyone know what would cause this. Also, are there suppose to be 1 or 2 fuel filters on this bike. It has the tube coming straight off the bottom of the petcock and going to the 1st and 2nd carb. The other tube goes to the 3rd and the 4th is filtered. Is that the way it is suppose to be? This thing also pulls alot of fuel through that 1st hose. Thanks for any advice.