petcock check valve

After thinking I had a major valve ticking problem (it was pretty loud) and doing some really careful listening I got my ear on the fuel tank and found the noise coming from there. After perusing the big manual, I figure the the petcock check valve is not working right or at all (I had the tank propped up while it was running and the bottom fuel line was starting to slip off and noticed the fuel leaking was actually pulsating out, the check valve is supposed to stop that so fuel runs smoothly to carbs). I pulled the petcock, took apart the diaphram side and saw black gook(for lack of a better term)in the center hole of the 3 where the check valve is located. Proceeded to get the gook out with carb spray (took alot of spray). Is the gook supposed to be in there? I put it back together, the ticking is still there but quieter. The o-rings and diaphram appeared to be in usable condition (no tears or cuts)and the spring appeared to ok. The petcock does work properly otherwise, gas flow stops when engine not running,flow starts when engine running. How do I make the checkvalve work like it's supposed to?

I don't know what you are referring to exactly. The petcock has simple holes in the lever that line up with simple holes in the body. When the lever is moved to different positions gas is either allowed to flow directly to the carbs or gas is sent to the diaphram where flow stops unless vacuum pressure from the engine draws the diaphram open. The only check valve type thing in the carb is the diaphram. If you disassembled the diaphram, cleaned it, and it still functioned you were extremely lucky. Normally once fooled with they will never seal again. If you have ticking coming from the petcock, about all it can be is a vacuum leak at the diaphram. Get a new diaphram for about $10 and this should solve it.

The ticking is definitely coming from the petcock and there is a check valve of some sort in the petcock diaphram cover, I don't know that changing the diaphram is going to stop the ticking sound. May have to try and find another petcock.

Can you point out what you are calling a "check valve" in the pic below?





14 "0" RING
15 SCREW-PAN-CRSOSS,4X1
16 WASHER SPRING 4MM
17 COVER ASSY,FUEL TAP
18 SPRING,DIAPHRAGM
19 DIAPHRAGM VALVE ASSY
20 "0" RING,DIAPHRAGM
21 GASKET,FUEL TAP
22 GASKET,DRAIN BOLT
23 BOLT,DRAIN
24 SCREW PAN HEAD 4X8
25 BOLT-HEX HEAD,6X16
26 WASHER-PLAIN

I assumed you are talking about the KZ1000 listed in your sig, since the 79 KZ750B doesn't have a vacuum petcock

Post edited by: steell, at: 2007/07/26 11:36

Ron, the check valve is located in #17 according to the manual. I took the petcock (#17) apart again and this time noticed that the round "washers" that sandwich the rubber diaphram were kind of bent up so I gently massaged them back flat to one another put it back together and the ticking was gone! However it wasn't completly sealing when the motor was shut down and I'd still get a little leakage from the #4 overflow. In the mean time I'd ordered a new manual petcock and pingle adapter from z1 ent. I installed it and like it very much. As a side note with the original petcock and the new petcock if the bike sat for more than a day I would have to crank the starter quite a bit before it would finally fire up. When I installed the new petcock I also replaced the fuel lines with clear yellow lines and filters. One of the mornings I was going to start it up I decided to watch the fuel in the lines when I opened the petcock and saw that a fair amount of fuel went into the carbs(don't ask me how much)until it filled to the filters(filters about 2" from carbs). So now when I open the petcock I wait 5 seconds or so the bike has since fired right up, no more long cranking. So, in retrospect I probably should have done what you suggested and rebuild the petcock with new parts and would have been money ahead and the convenience of vac operated petcock but taking off the tank is easier with just one line instead of three.