Rebuilding the Yamaha Vacuum Fuel Valve w/pics

Anytime, happy to help.

As many of them that I've had apart, I've never seen any sort of adhesive residue on the standpipe. I suspect a PO. Being super fluid-tight is not an issue (think about it) the main thing is that it doesn't come "unstuck" and drift about.

 

Can I purchase a simple on off reserve valve for my XJ550RJ 1982 ?

 

Had to rebuild the (highly unusual and expensive) FJ petcock. I was reluctant because I had read a couple people's experience of thorough cleaning and rebuild resulting in failure, but then I realized that the replacement petcock was normally $225, there was one guy who was selling NOS for $175, and an on-off version for $125.

So I replaced the plunger o-ring and cleaned stuff up. No dice. Then, on a burst of inspiration, I put in a small rubber washer to add pressure to the spring (which supposedly was replaced a year before by the PO).

Bam. Works perfect--seals well, flows well. No problem a thousand miles later. Thought it was a novel fix...

...But sure enough, Fitz has already written that into his guide.

Anyways, a video that I relied on for inspiration and education: https://www.youtube.com/watch?v=5DqvB_5 ... ata_player

 

Headed out to do this very task , wow it looks complicated now !

 

This might sound like a dumb question, buuuut...How did you guys determine that you needed to rebuild the petcock in the first place? Gas in the oil? I just got a Seca, and want to know what to look for. Post #1 AWAY!

 

lacucaracha
There are many ways a petcock could leak: from the back plate, from the selector in the front (those you could notice easily) and from the outlet when the engine is off. You won't notice that one if your floats work properly, but if not, your carbs will get flooded and you may end up with gas puddles on your garage floor and/or gas in the crankcase.

It is often what is the starting point for a petcock rebuild!

 

Great, thanks for the info! I'll check that as soon as my bike is back from getting new rubber!

 

Yes gas in oil and gas stain on side covers from leaking fuel system

 

So I had rebuilt this over a year ago and all was good. Now fuel pushes out the channel to the rear of the bike with vaccume connected but does not with vaccum disconnected! Any suggestions?

 

If you're talking about the little vent hole in the plastic spacer plate; if fuel is coming out of there it is on the "wrong side" of the diaphragm.

The fact that it only does it under vacuum indicates that the valve does shut off correctly; but once opened it is allowing fuel to get where it ought not to be. About the only way that could happen would be a damaged diaphragm if the petcock was reassembled correctly and had been working fine.

 

Timely this article pops up on my radar as I put the tank on the bike for the first time in 4 years and no gas is flowing to the carbs! It looks like a tear down is the next thing on my list...

 

Timely this article pops up on my radar as I put the tank on the bike for the first time in 4 years and no gas is flowing to the carbs! It looks like a tear down is the next thing on my list...

 

The diaphragm must be damaged, the rebuild held for over a year then sat while I messed with my new bike. The diaphragm looked alright but can it break down from sitting?
I did notice the small disc missing that is supposed to be somewhere at the vacuum port. I did not see this in the rebuild kit only now spotted it in the rebuild photos. Could this be the issue?

The vacuum port check valve

 

I was tearing down my spare petcock as I prepped a shopping list with Len, and I came across "HCP19586 Aftermarket petcock vacuum diaphragm CHECK VALVE."

I see now that it's in the second picture, but prior to that I was racking my brain trying to figure out what part Len's catalog was referring to.

It's a super tiny wafer that didn't fall out when I removed the brass vacuum nipple. I decided to take the liberty of snapping a few up-close shots and share them here for others to reference. Fitz, feel free to steal one or both.

 

Precisely.

This thing:



(From the rebuild article above.)

Very important little bit. If it's missing, damaged or stuck in place, the petcock won't function properly. Without it, the diaphragm would "hammer" back and forth and prevent the steady flow of fuel.

No need to "steal" the pics, you've contributed an excellent real-world closeup of the silly little thing. What's amazing is how simple yet important it is.

 

Proving that it's the little things in life.

 

Think about it for a second. That may be the smallest critical moving part on the whole bike. If that tiny little disc fails to do its job, ain't nobody happy.

The even-tinier hole in the bottom of the master cylinder is arguably as important; but it doesn't move, it's just there.

 

I'm resisting the urge to draw parallels to GMC's ignition switch woes. I show amazing resilience, don't I?

 

lost my vacuum port valve(the tiny bakelite disk)any ideas how to replace it??? do i have to buy a new petcock???thanks

 

E bay sells parts , rebuild kits , or new and used whole pet cocks