petcock problems

1979 KZ650 petcock would flow fuel in all positions, so I assumed that it needed rebuilt. After rebuilding, it does the same damn thing again!!!! Any ideas/suggestions?

medic24 wrote:

1979 KZ650 petcock would flow fuel in all positions, so I assumed that it needed rebuilt. After rebuilding, it does the same damn thing again!!!! Any ideas/suggestions?

Out of curiousity, what are the poisitions? I mean is this a vacuum or old-style gravity?

I'm going to have to ask this question. What is the purpose of shutting off the fuel valve when the bike isn't running?

Understandably, if you're taking the tank off, you don't want it to leak, but as far as general running, unless you have a leaky carb, is there any need?

The reason I ask is that I believe my petcock does the same thing. I learned this when I had my first experience of gasoline making a hissing noise when hitting a hot engine block. * COMPLETE PANIC! *

Vacuum petcock.

the "O" ring that seals the petcock off while it has no vacum is not sealing, be it from wear or a piece of trash under it.

or the spring that holds the diaphram shut has failed.

Sometimes a float valve will get stuck in the open position by friction or a piece of dirt. When riding the vibration will overcome the friction and the fuel flow will wash the dirt on through. Shutting off the petcock while your bike is stationary prevents all your gas from running through onto the ground.

mind2find wrote:

I'm going to have to ask this question. What is the purpose of shutting off the fuel valve when the bike isn't running?

Understandably, if you're taking the tank off, you don't want it to leak, but as far as general running, unless you have a leaky carb, is there any need?

The reason I ask is that I believe my petcock does the same thing. I learned this when I had my first experience of gasoline making a hissing noise when hitting a hot engine block. * COMPLETE PANIC! *

del

The petcock is really a dang simple mechanism. The lever controls which tube fuel is drawn through and the diaphram is held open by vaccumm to let the gas flow in the on and reserve positions. Either you've not got the diaphram assembled just right, your diaphram spring is missing, or you simply got a bad new diaphram. I assume in rebuilding the diaphram was what you replaced? They can be a major pain sometimes. I've never in my life disassembled one of these and put it back together and have it work. If taken apart a new diaphram is needed every time, the oring aint going to fix anything.
As already mentioned on the other question on why you need to turn gas off, you never need to in a perfect world. If your needle/seats seal 100% no problem will ever come in leaving the gas on. Trouble is it's not a perfect world and the needle/seats can seal great one day and not the next which results in the big gas spill on the floor, which is not a good thing.

del

Hey guy, thanks for the info so far. Well here goes....diaphram spring? huh.... Maybe I missed something. DOH! Was a K&L kit and I "thought" I replaced everything I found in the petcock. GUess I better look again.
Dave