A note on petcock repair kits...

[dbeardslee]

I purchased two petcock repair kits from Partsnmore last fall, and they remind me of the old Maxwell Smart line - "missed it by that much."

The kit had everything with the exception of the spring that pushes against the rubber diaphram to shut the fuel off. With a new o-ring on the plug in the center of the diaphram the old spring just didn't have enough strength to fully seat the o-ring and subsequently it didn't shut the gas off like it was supposed to.

The fix was relatively easy. I went to ACE hardware and found a stainless steel spring of the correct diameter and approximate same "springiness". The springs were much longer than the originals so I cut them to size (slightly longer than the old ones), installed them, and the leaks stopped.

One thing to watch for is that, if the springs are too long or too strong, the vacuum may not be able to pull the diaphram back, in which case you need to shorten the spring or run in the prime position.

Mine work great in the normal running position. It will push tha tach as far into the red zone as you care to take it without starving for gas, and when I shut it down there's no gas dribbling out.

[Kevin W]

DB,
I've been fixing a few petcocks too. I was having the same problem as you and decided to do a little "experiment". I put a few spare plunger O-rings into a jar of gas and left one out for comparison sake and found that the ones in gas had swelled noticeably. I haven't put the petcocks back together yet or leak test, but I'm thinking pre-soaking is the trick. I'll let you know.
KW

[TopCatGr58]

Hey Kevin,

Spare "Plunger" O-rings?? If these are just some spare O-rings that you got from a hardware store, they may be regular natural rubber, and so, yes they will swell, but they will also be ruined! The VITON or Neoprene type O-rings that are designed to be used in the presence of fuel should NOT swell!
T.C.

[dbeardslee]

I'm glad to hear the neoprene is the stuff to use around gas. I replaced the philips head bolts that attach the petcocks to the tank with hex-heads, and when I did I used some small neoprene washers on the bolts. I was kind of wondering when I did it how well they would hold up to gas.

I've never tried soaking o-rings, but I have tried soaking the funny shaped o-ring/gasket that goes between the petcock and the tank in floor jack oil. It said on the bottle that it reconditioned seals, so I thought "what the hey, it's worth a try."

This was before I rebuilt the petcocks, and they were the original 28-year-old parts. I don't know if it did any good, but they didn't leak at that spot, so maybe it helped.

[Kevin W]

T.C.
I bought the O-rings from my local yamaha dealer and told them at the time that I needed GAS o-rings. The counter guy brought out a case of O-rings and we compared them with one I took off an extra petcock. Paid $2 each. I understand that some rubber O rings, and seals are made special for different fluids like brake fluid and gas. Do you think if they were the wrong rubber they would continue to swell to the point of being totally worthless?
Thanks
KW

[ExcessiveBiker]

Petcock Kits

The problem with some rebuild kits is not the spring or the O ring, the post is too short. I found this with some 750 kits on my '76 XS. The center post riveted to the diaphragm is approximately .030" shorter than the stock post. The fix was a larger cross section O ring to take up the slack from the post. Don't remember what size worked, but trial and error should find the size. Too small and it leaks, too large and it won't let fuel through.
happy rebuilding,
ExcessiveBiker

[skids]

Re: Petcock Kits

I suppose you could suck on the vacuum hose while the wife blows on the fuel input line as a test. (This was not meant to be funny)

Originally posted by ExcessiveBiker
The problem with some rebuild kits is not the spring or the O ring, the post is too short. I found this with some 750 kits on my '76 XS. The center post riveted to the diaphragm is approximately .030" shorter than the stock post. The fix was a larger cross section O ring to take up the slack from the post. Don't remember what size worked, but trial and error should find the size. Too small and it leaks, too large and it won't let fuel through.
happy rebuilding,
ExcessiveBiker

[bikerphil]

test

Yes, but it was funny! Pics. please!

[Mashermoto]

Spring in the petcock...Hmmmm

My 78 XS750 that pours fuel out the petcocks regardless of the position didn't have a spring

Dbeardslee, if your out there, what spring did you get from Ace and how long did you cut it

[dbeardslee]

Masher- take the diaphram with the plug in it to Ace. If it's layed out like the one here, there will be an isle with nuts and bolts and assorted other stuff, like springs. On the back of the diaphram (the side away from the o-ring) there is a little protrusion. The spring fits around the protrusion. Just find a stainless steel spring of the proper diameter to fit snuggly around the protrusion. I don't know the exact size of the springs, but they were about 1.25 - 1.5 inches long. I basically cut one spring in half. Put the factory end around the protrusion and the cut end in the hole in the cap. Make sure the o-ring on the plug is in good shape, and put it back together.

[dbeardslee]

Masher - I was up at ACE today (my home away from home) and got the specifics on the spring I used. It was in bin #123 and it's a 1.25" X 3/8" X .025" compression spring. Very light gauge. Again, cut in half it will do both petcocks.

[Mashermoto]

Dbeardslee,

I have to apologize profusely

My rebuild kit came in from PartsNMore today. I disassembled the petcocks and both had the springs

Well...they say the mind goes first

But I really appreciate you researching the spring, I may have to do some modifications with a replacement spring if I can't get a good shut off.

Maybe I can return the favor in the future

[dbeardslee]

Masher - no sweat. I was up there anyway. There's another post on petcocks around here somewhere that mentioned the other side of petcock - where the lever is. There's a spring in there too, but it's a different kind. It looks like a wavy washer. Evidently those get weak too and the fix is to bend them a little (not too much) more. I did it on mine when I rebuilt them. Also had to do with leaks, if I remember correctly.

[mro]

I've rebuilt several standard petcocks with kits from bikebandit.
No problems with any so far and last was done a few years ago.
Used original springs too.
One thing tho is to clean and polish the flat surface inside the petcock, petcocks handle.


mro
bTW,
they have gone up in price, from $20.00 ea
to I think $38.00 ea now

[manshack_one]

http://www.bikebandit.com/product/A6548333

I've got an '80 special and need to rebuild the right hand petcock. If this is the kit you used, did you end up needing all 3 parts like they show in the picture?