Petcock leaking fuel from diaphragm area

Hello all,

I just rebuilt my petcock with a K+L brand rebuild kit and it’s leaking fuel from the diaphragm area pretty bad. Took it back off and double checked my work using the service manual and it’s still doing it.

the fuel filler cap is hissing too, so it would seem the vent may be slightly obstructed and causing pressure in the tank. Is it possible the vent issue is causing the petcock leak by pressurizing the diaphragm? 1982 Spectre 1100. Thank you!

I don't think so. If tank pressure built up and the petcock was sealing properly, then the pressure might force the valve open a bit, sending fuel to the carburetors.
I think it more likely that you have multiple problems, the vent being one.
In order for fuel to escape, there must be at least two failure points, the oring and it seat, AND either the diaphragm or the round rubber washer under the selector lever.
Did you carefully polish the seat the oring presses against? The slightest irregularity in that surface can prevent a seal.
Are the sealing surfaces of the valve smooth, flat and free of even tiny defects?
Was the diaphragm improperly installed on the metal plunger, thus leaking?
Did you carefully inspect the selector lever's face for pitting? It should be hand polished on a flat surface before reassembly.
I would take it apart to inspect and polish, then give it another try. When you get it apart, post some pictures so maybe one of us can see what is going on.

If the problem is the replacement parts, the supplier should warranty them. If the petcock body is badly pitted, replacing it may be the solution. Though a bit pricy, Partzilla shows the assembly as still available from Kawasaki.
 

Try searching the forum. Somewhere around here is a link to a good tutorial that was posted on one of the GS forums. It has pictures of all the important bits of the process.

Yamaha but applicable to Kawasaki's as well. 
Petcock rebuild tutorial

More relevant stuff. Gotta ask, why the rebuild initially? Beyond that did you install the "wafer" correctly? One side is dished, other flat. Also, those wafers that separate petrol from vacuum diaphragms,  have locating tits. Diaphragms are often oriented where only 1 of the 4 positions are correct. Are you sure it's weeping from the casting halves or just drizzling down from tank connection? Something noteworthy too, those petcock casting can warp. See last photo where blue pointer against a flat surface is, this one shown is bowed/warped. This will allow vacuum and petrol loss. Also verify the diaphragm aluminum protrusion cannot be turned within the two rubbers. Sometimes they are not crimped correctly, i do a lot of chainsaws, same principal. I'd quit rebuilding these petcocks unless absolutely necessary because of rarity. Often, which you've not gotten there yet but those aftermarket kits' protrusion with oring don't sit perpendicular to the beveled oring seat TexasKZ was talking about. Maybe this crap will help??      

Here is a quick video of what it’s doing:

youtube.com/shorts/_iJSH-2OEQA?si=VPT0z1X7nckAVvIe

It’s popping occasionally and spraying fuel out of the small port as you can see in the video. You can also see the glistening of fuel around the diaphragm sandwich.

I will take the petcock apart again, though I’ve had it apart 3 times now and looked closely and everything is clean and not pitted. I can take some pictures and see what you guys think. 

Some people are saying the K+L petcock rebuild kit isn’t right and that it has to be altered to work correctly, but that’s for a Yamaha bike that I was reading about. They can make mistakes though it seems. I’ve gone ahead and ordered all factory parts for the rebuild, the K+L kit makes the petcock very stiff to operate.

Legionnaire1856 wrote:

Hello all,

I just rebuilt my petcock with a K+L brand rebuild kit and it’s leaking fuel from the diaphragm area pretty bad. Took it back off and double checked my work using the service manual and it’s still doing it.

the fuel filler cap is hissing too, so it would seem the vent may be slightly obstructed and causing pressure in the tank. Is it possible the vent issue is causing the petcock leak by pressurizing the diaphragm? 1982 Spectre 1100. Thank you!

Just an FYI - vent issues will cause a "vacuum" in the tank not "pressure" the hissing you are hearing is suction. Therefore there is no pressure being applied at the petcock (the opposite in fact)

Wookie58 wrote:

Legionnaire1856 wrote:

Hello all,

I just rebuilt my petcock with a K+L brand rebuild kit and it’s leaking fuel from the diaphragm area pretty bad. Took it back off and double checked my work using the service manual and it’s still doing it.

the fuel filler cap is hissing too, so it would seem the vent may be slightly obstructed and causing pressure in the tank. Is it possible the vent issue is causing the petcock leak by pressurizing the diaphragm? 1982 Spectre 1100. Thank you!

Just an FYI - vent issues will cause a "vacuum" in the tank not "pressure" the hissing you are hearing is suction. Therefore there is no pressure being applied at the petcock (the opposite in fact)

Could moving the bike from shade to sun, or rising temperatures in the afternoon, or heat from the engine create pressure in the tank?

TexasKZ wrote:

Wookie58 wrote:

Legionnaire1856 wrote:

Hello all,

I just rebuilt my petcock with a K+L brand rebuild kit and it’s leaking fuel from the diaphragm area pretty bad. Took it back off and double checked my work using the service manual and it’s still doing it.

the fuel filler cap is hissing too, so it would seem the vent may be slightly obstructed and causing pressure in the tank. Is it possible the vent issue is causing the petcock leak by pressurizing the diaphragm? 1982 Spectre 1100. Thank you!

Just an FYI - vent issues will cause a "vacuum" in the tank not "pressure" the hissing you are hearing is suction. Therefore there is no pressure being applied at the petcock (the opposite in fact)

Could moving the bike from shade to sun, or rising temperatures in the afternoon, or heat from the engine create pressure in the tank?

Possible I guess if the temp difference is great enough, could always park it with the gas cap open and see if it still leaks ? (Only my opinion but I would think a reasonable amount of pressure would be required to cause a leak)

Watched the Video You Utube star!! You have a couple issues. One is the obvious weeping and spitting. This is because the main body is warped or the plastic plate is too, or cracked. That little cut-out states it all, no correct sealing. The other is "why" would it sporadically be spitting to begin with? That is because the "check pad or ball" isn't sealing under pressure when your cylinder spits back. those check valves or reducing jets are built into All these Vacuum petcocks, just have to know where to look.     Don't waste anymore time and just purchase a New one. Or machine flat the main casting and double check the plastic wafer. Pick your battles wisely..