Rebuilding the Yamaha Vacuum Fuel Valve w/pics

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

 

Scroll up about 5 posts, BaldWonder and bigfitz52 show the part. BaldWonder even lists the part number from Chacal - email him at info@xj4ever.com for the best parts and service you will ever find for these bikes.

 

PM Chacal.

 

What are the pros and cons of switching over to a non-vacuum on/off switch?

 

Pros: less to go wrong
cons: you ALWAYS have to remember to turn it both on and off every time you start or stop the engine!

 

Knowing my short term memory problems, that sounds like a recipe for disaster....

 

Chacal; how much for a 1982 xj650 rebuild kit?

 

How ya doing all, new here,Great post Fitz, just bought an 82 midnight maxim, had been stored indoors for 3 years then outdoors in wet for a year before I got it, there was only a little juice in the tank was riding on reserve put 10 litres in it did about 40 miles and phut phut phutted to a stop I could hear fuel in the tank when I shook it but wasn't coming through the reserve position petcock I managed to get some fuel about 4 litres left it in reserve got about 1 mile down the road and died again, put it in primary and was grand topped the tank up, clocked the clock and today happened again only got 70 miles on full tank, and got stuck in the middle of nowhere for a while till I could get more juice in to get home, so I can physicality see petrol in the bottom of the tank but reserve position not working at all, is the reserve blocked? I also noticed a strong fuel smell when I did fill the tank but no visible leaking that I can see, could this be petcock related? many thanks

 

Max.. you will be better off starting your own post about your bike in Technical chat where all the questions and info' will be together and others can follow what you have / haven't done.

Have you taken the fuel line off the tap and seen what is happening at Pri Res and Off. Checked the breather in the fuel cap is clear. Completely drained the tank .."outdoors wet for a year ".. could be water sitting in the bottom. It sounds like time to start on the catch up maintenance.

 

Hey, I'm in the middle of trying to get the petcock on my 750mk to stop leaking, but for some reason the pictures in the main post just aren't there. I remember there being so many great pictures of the process but now it's a wall of text. Were they taken down, do they load for everyone else?

 

I see all of the pictures. Perhaps there was a server problem, or your browser needs to be updated.

 

How do you remove the in tank filter from the petcock? I've tried gentle pulling, with no luck, I don't want to break it, it is still in good shape. is it glued in or clipped in?

 

They are held in by a light press fit. If it's in useable condition it does not need to be removed. Most of the time they are not in great shape and will fall out on their own.

 

Ok..thanks.

 

Ian Vanore Thank you SO much. you have saved us all from the great photo bucket FU of 17! The write up was copied with permission to the XS650 forum and to my horror all the pics were lost, UNTIL I found your PDF link, WHEW!!!! That has now been saved as file on the XS650 forum with a credit to you Ian, hope that's OK, G

 

Ian, did Fitz give you permission to copy and re-distribute his work?

I'm rebuilding his forums right now, and I DO have permission from him.

Dave F

 

Really great post. Thought I was gonna have to cower and send it to the mechanic to fix. Nope. Just had to read a few times, get supplies, and dedicate two hours to. Of course, Len crushes it. Should've taken a pic of the packaging for the deluxe rebuild kit. Sleek, well organized. Got it rebuilt and reinstalled. No leaks. Took a ride, felt great. Thanks a bunch, guys.

 

I just finished building my leaky petcock, after ordering a rebuild kit. I should have ordered from from xj4ever... but using some permatex Motoseal closed those up without leaks so far. I dressed practically every part. Also I put In in line valve (1/4 inch from Home Depot) just to make sure no extra fuel was getting past the petcock. It works very well, and isn’t too visible.