Fuel in the Airbox

[Incubus]

Believe me, Mike, I cleaned and polished every surface. They couldn't have been more sanitized in Antartica. Drip, drip drip. I bought the rebuild kits from PNM. Drip, drip, drip.

I have later read that some rebuild kits don't work well because the peg through the diaphram isn't long enough. The ones that were in the petcocks when I got them are the same way.

I bought aftermarket petcocks with an "off" position. I think they're from an xs650.

I still have the old petcocks. I keep them around just to hate them. It's hard to give up a hate this pure.

Patrick

[wa407mpp]

cleaning petcocks!

When you clean the petcocks do not! repeat do not! polish or clean off the gray film inside the petcocks, it is a sealer and was put there at the factory to seal the aluminum so it won't leak. If you polish it off it could cause them to leak even worse then before. The rebuild kits should have had new springs to replace the ones that have weakened over the years that's what causes them to leak by, weak springs and hardened rubber gaskets.

[79XS11F]

I got fed up with my fuel petcocks so I bit the bullet and bought 2 new units. I will install them on my restore bike and use the questionable ones on the hop up bike.
Rob

[Ken Talbot]

Re: cleaning petcocks!

Originally posted by wa407mpp
that's what causes them to leak by, weak springs and hardened rubber gaskets.

I've found the biggest problem with petcocks on a standard is a plugged spooge hole.

The way they are built, vacuum is applied to one side of the diaphragm. This pulls the rubber o-ring, on the aluminum stud in the middle of the diaphragm, away from the seat which allows fuel to flow. When there is no vacuum behind the diaphragm, the spring pushes the o-ring back into the seat and shuts off the flow of fuel. In the body of the petcock, on the vacuum side of the assembly, there is a small orifice that bleeds off the pressure or vacuum behind the diaphragm. If this is orifice is plugged, the vacuum does not release from behind the diaphragm, even when the motor shuts off. All the time the diaphragm is pulled back, the fuel keeps flowing. If the float valves are also defective, you now have flooding problems.

Clean the spooge hole, and test the petcock operation. Disconnect the fuel line from a carb and run it into a jar. Apply vacuum to the vacuum nipple on the petcock and you should see fuel flow. Release the vacuum, and the fuel flow should stop immediately. Immediately as in right now, with no tapering off or dribbling.

I can't quite visualize how there could be some sort of film on the inside of the petcock body that would be meant to prevent fuel from leaking through the aluminum body of the petcock. Is this the film you're talking about?

[79XS11F]

I would guess that the film that is talked about is the gray RTV sealant applied by a PO that should not be needed if the seals and diaphragm is in good and usable condition.
On a petcock rebuild they should be cleaned as you would do you carbs. they need to be spic & span so to speak.
Rob

[wingnut]

Dry Film Lube

The gray stuff could be a dry film lube compound. Its often used on air and fluid valves by manufactures to get a good seal. You can get it in a spray can from an industrial supply house. Did't notice it on my special petcocks though

[wa407mpp]

The gray film is a sealer applied at the factory, There was a warning printed in the factory rebuild kit I bought from the locale Yamaha dealer, it was not something applied by a PO, I know this because the PO was a personal friend of mine and I did all of the maintenance on the bike scene it was new. That's one of the main reasons I bought this particular bike, I knew the original owner and the maintenance history, and I know for a fact, that when I rebuilt the petcocks was the only time they were ever disassembled. Perhaps if the film is missing from your petcocks it was removed by a PO.

[skids]

I have sanded and polished the faces of all three of of standards petcock (valve handle) faces to a mirror-like finish. I also took the edges off of the holes to help prevent wear on the holey gaskets. This is the best thing that I have found to make petcocks last longer. The conical seats should also be posished to get the corrosion out and make the plunger seat better.

[mro]

read that some rebuild kits don't work well

Had read that too and was a concern that I might have wasted money spent on em.
Kits I've used were the chee...er..least XSpensive ones I found.
Have done 3 sets of standards and all worked well.
The "film" being talked about might be "anodize"???
Does polish nice and smooth.


mro