Need help with fuel petcock, leak, leak, leak

Well I thought the worst of my problems would be electrical, but they have come along with little trouble. Big trouble is the beloved petcock. I rebuilt it a few months back did not put gas in tank to check, how difficult can it be? Well, apparently difficult. Problem is no mater what position the valve is in pri, res or on I get gas. The least is at the on position, just a continuous drip. Will not stop. I have researched & found the petcock rebuild thread. I have torn it apart at least six times all with the same result. Still leaks. I did find I had the diaphram installed wrong, did have the plastic between the 2 sides of the diapram seal. What did I do incorrectly? Or do I need a new petcock? Any help would be appreciated

 

Was this a new kit ?
You might try replacing the O'ring and clean the seat real good.
Check/Add Spring tension.

 

Richard,
Yes it was a new kit. When you say add spring tension do you mean stretch the spring a bit to increase pressure applied to the diaphram?
I appreciate the help.
Gregg

 

I rebuilt mine but the seeping into the carbs persisted so I used a washer that goes in with the spring offered by Chacal, that worked perfect for me.

 

Rpgorlich is correct.......both the o-ring on the end of that vacuum plunger tip must be good (soft), and, especially, the bevelled, machined SEAT in the carb body that the o-ring contacts must be in almost perfect condition......no gouges, scratches, missing metal, rubber build-up, etc. The failure of that o-ring to FULLY seat TIGHTLY against that seat is what causes that "drip-drip-drip" from the fuel outlet, which can lead to all sorts of problems.

The original o-ring on these plungers were actually hollow, which allowed the o-ring to deform a bit under the spring's pressure and create a perfect seal again that seat. The replacement o-rings that come with the petcock rebuild kits are solid, and therefore much less "forming" to any imperfections in that machined seat. The old spring may also create reduced pressure, and all these factors can contribute to the problem. The small "shim washer" that I offer goes under the spring and helps to restore some of the spring's pressure; sometimes (as with Nemo's experience), that is enough to solve the problem.

One thing you need to do is inspect that machined seat carefully, I recommend using a magnifying glass, as ANY surface scars or imperfections are the main cause of 99.9% of "petcock leaking" problems after they've been rebuilt. You have to get really anal in looking at that seat; it must be smooth. If there are minor flaws, you can sometimes polish them out with a wooden golf tee and some ultra-fine grit valve lapping compound; if the flaws are deep, then that petcock body is toast, and you look for other solutions (replace the petcock, install an in-line on/off valve, etc.).

 

Chacal, Nemo
Thanks for the input. I did a little stretch number on the spring & did some cleaning of the seating area for the plunger & so far it seems to be working. I do not have fuel showing 1/3 full on the inline filter. So I think I got it for the moment. Next problem is getting enough juice from the battery to get the thing started. I tried what I thought was a good auto battery to jump it but that didn't get it done either. We will try again tomorrow. I started this project some time back, just about got it ready, only need it to atart & get a MC rebuild kit. But unlike the bike, the parts aren't free. I appreciate all your input & any further suggestions will be deeply appreciated.

 

Oh fer chrissakes, as in a tiny little circle of HOSE? I never even knew such a thing EXISTED but leave it to Yamaha to use something that exotic in such a TINY yet mission-critical application. And of course THOSE aren't used anywhere since and probably aren't even available on the open market. Talk about "unobtianium."

One is reminded of the $28 bearing that ended the debut of the STP turbine Indy car...

 

Yeah, kinda exactly like that!

Actually, it was the company that made the petcocks (Taiyo Giken) that made them that way, and they were a supplier of petcocks to many different OEM's, not just Yamaha. I don't think we can blame The Big Y for this design!

 

Well, the problem persisted so I fabed a washer to go in under the spring (thanks Chacal) & also clean a slite bit of residue on the mating surface for the o-ring. I have reassembled & put tank back on the bike, have gone 20 min & no gas going into the inline filter. I think we have it. Thanks guys for your input it is beyond value, kinda like the credit card commercial, priceless.
Fitz, I remember the STP turbine story very well, I was there. It was incredible how much faster that car was than the rest. At the end of the 1st lap he was 1/2 a lap ahead of 2nd place. Incredible.

 

I cleaned my pectcock and is working fine but when you metion the position of the diaphragm It catch my attention. I do have the plastic on in between the 2 sides of the diapragm. It works fine. Should I correct that?
BTW do you have the link for the the petcock rebuilt thread?

Thanks,

Carvall