leaky petcock - please explain

[schpiff]

I think I saw petcock rebuilds at bike bandit...http://www.bikebandits.com/

[Snow]

partsnmore has them for about $13 each, usually takes about a week for UPS to get them from Canada to Florida for me.

[RiskyBusiness]

Originally posted by Snow
partsnmore has them for about $13 each, usually takes about a week for UPS to get them from Canada to Florida for me.

Are the specials different WRT petcocks? I have a special and have been hesitant to get the kit from partsnmore. Anyone know?

[beechfront]

i couldn't find anything at bikebandits. the partsnmore page doesn't list them for a 79 special.

[schpiff]

Hi beech, This is what i found at bike bandit
The clymer manual i have shows the same petcock (at least appearance wise) for a '79 as wel as an '81..
I Had to use the '79 xs650 for the search..but the part number shows up for both.Part nunmbers and prices...
81sh.."fuel valve"..p# 3h3-24523-00-00 $7.91
79 650sh..Fuel "gasket?" p#2g2-24523-00-00 $7.94.....
THe number24523 shows up on both (as well as any yamaha special search).
The exploded view shows the same 5 hole piece of rubber...I am willing to bet that the first numbers are their year/bike code and the middle numbers are the actual yamaha part....
MY ADVICE IS IF YA NEED EM BUY EM..IF I AM WRONG I WILL BUY THEM FROM YOU
By the way..when you have the petcock apart rebend the "wave" washer a little bit..I had to do both sides again cuz the washer wasnt keeping things as tight as it shoulda..(no more gas fingers when moving the lever)

[beechfront]

Re: Petcock theory

Originally posted by Jerry
Petcocks were designed to perform several functions. First, they shut off gas flow when you want to unhook the gas lines to remove the tank or carbs. (Off function.) Second, as a safety feature, they shut off gas flow when the engine is not running, preventing gas from flowing out of the tank in case of an accident. (On function.) Third, they provide a bypass operation to allow fuel to flow at any time, ususlly used to fill the carbs after a cleaning or service (Prime function.) Forth, they allow you to access the reserve fuel in the tank when you start to run out of gas. (Reserve function.)

I am confused as to what is all included in the term petcock - I refer to the petcock as the two valve devices (one on each side of the gas tank) which allow/stop the flow of fuel from the tank, and not including the octopus unit.



What I am confused about is whether or not the term 'petcock' includes the octopus or not. On my bike, (1979 Special) there are two outlets on each petcock - one flows gas when turned to the 'on' position (regardless of whether or not the engine is running) and flows to the octopus unit. The other flows when turned to the 'prime' position and bypasses the octopus. The octopus has two lines running in (one from each tank's 'on' position) and two lines running out to the carbs. There is an isolated line on top which hooks into the #2 manifold for vacuum.

So my question is..... am I looking for a petcock rebuild kit or a rebuild kit for the 'octopus' device? Because I belive my petcocks are working just fine - I believe the problem is in the octopus.

Is the function of the octopus built into the 'petcock' device on some motorcycles?



Any thoughts?

[fusionking]

Beech ,dude get a manual cause as neat as this site is there are some things that can't be told very well by question & answer. I have both the genuine YAMAHA & the Clymer. Some things they are the same on & others the factory just expects you to know stuff because it they wrote their book for dealers. Sometimes Clymers has a better approach. When I attempt a new task I have both manuals open & everything from the tips section printed out also! You really can't have too much info on hand! Anyway what I'm driving at is, I think Clymer tells how to check the octopuss by sucking on that very vacuam hose you was talking about that hooks to #2 manifold. Also on the petcock rubber deal with the holes in it , I just went up to my buddy's bike shop & he motioned me to a big assortment of them. I picked out the pair I needed & it cost me like $8.00 . They are generic & cheap! All I really want to do is ride my bike not work on it. Garry

[schpiff]

Another option that has been discussed here on the forum is deleting the "octopus or spider" I have been thinkin about it myself. The fix is pretty straightforward. Just use a "tee" on each side so you only have 1 hose from each petcock. This eliminates the "octopus..or spider" BUT MAKE SURE YOUR NEEDLE AND SEAT ASSEMBLIES WORK! AT LEAST MAKE SURE WHEN YOUR PETCOCK IS OFF ITS REALLY OFF! (says mr 4 gallons of gas in the crankcase....some on the floor)
With the "tee"... off is off, pri and reserve are the same, and on is just that....just like stock..just a simplified version, without the vaccum leaks

[beechfront]

I am considering bypassing the octopus - will play with it a little more and if I can't find a rebuild kit that's probably what I'll end up doing.


fusion, dude i do have a clymer manual. problem is nowhere in the 'petcock' section does it actually use the term petcock (pg 153-155). It refers to them as 'fuel shutoff valves' and 'vacuum diaphragm'. perhaps i'm looking in the wrong place, but when i look for a repair kit all i find are 'petcock' repair kits. my question is does a petcock repair kit fix the fuel shutoff valves, vacuum diaphragm or both because i think the problem is with my diaphragm.

The book does make reference to two kinds of valves. regular, and vacuum controlled. I think the regular valve has no vacuum control at all (fuel either on/off to the carbs), and in the vacuum controlled valve the control is actually being done by the diaphragm.

I realize I'm asking a lot of questions, but for now - unlike most people - I do want to work on my bike as much as I want to ride it. This is my first time with the bike apart and want to learn how everthing works.

[Ken Talbot]

Petcocks 101

The petcock repair kit looks like it gives you:
- a petcock seal 1J7-24534-00
- a petcock valve 1J7-24523-00
- an o-ring 1J7-24512-00, and
- a gasket 1J7-24522-00

Now here's where it gets interesting. There is also another piece included - the double diaphragm that actually provides vacuum control of the fuel flow. It is usually a problem with this part or a weak spring behind it that causes the petcock to leak fuel into the carbs, then into the airbox and crankcase. A weak wavy washer or a perished valve could cause a bit of fuel to dribble from the body of the petcock but neither of these will result in fuel flowing to the carbs when the motor is not running.

This diaphragm is a critical part of the petock on a standard. It is also the piece in the octopus of a special that provides vacuum control. And, I now know that the diaphragm from a petcock repair kit can be made to work in an octopus. Check out the following:

Here is a shot of an opened-up octopus:
[img]/forum/images/tips/20030406-dsc02105.jpg[/img]

And here is an opened-up standard petcock:
[img]/forum/images/tips/20030406-dsc02106.jpg[/img]

Here is the working end of the two diaphragms. The o-ring is what cuts off the fuel flow as the spring behind it pushes against it. It is only when the engine is running and generating vacuum that this part is pulled back to allow fuel to flow. About the only difference in these two units is the location of one or more small holes which provide a vent to atmosphere to allow the rubber diaphragm to move. In the unit from an octopus (left) there are four holes just inboard of the top and bottom screw holes. In the unit from an '81 standard petcock, there is a single hole at approx. 2:00 o'clock.
[img]/forum/images/tips/20030406-dsc02107.jpg[/img]

Even from the other end, the end where the spring pushes, both of these units appear to be almost identical. By swapping the two units back and forth between a petcock and an octopus, it is clear that the diaphragm from a rebuild kit can be made to work in either. A person only needs to pay a bit of attention to the location of the vent holes of the unit being worked on, then alter the diaphragm to suit.
[img]/forum/images/tips/20030406-dsc02108.jpg[/img]

Finally, here is a shot of the springs from the two different units, octopus on the left and petcock on the right. The spring from the petcock was noticeably weaker than the spring from the petcock, and I'm pretty sure that is what has been causing my petcock to leak. I have picked up a packet of generic springs from the local auto parts store and have cut them down to fit my petcocks. I checked them with a vacuum pump and verified they are not too stiff, i.e that the diaphragm can still push them back to allow fuel to flow when it should:
[img]/forum/images/tips/20030406-dsc02109.jpg[/img]

Summary:
- if your petcocks or octopus are allowing fuel to flow when there is no vacuum, you probably only need to replace the spring unless the diaphragm is torn
- if your petcocks are dribbling around the handle, you need a rebuild kit for the seal and valve
- you can use the diaphragm from a petcock rebuild kit to rebuild an octopus

[beechfront]

Ken I cannot thank you enough for the generous information. Really saved me a headache.

[beechfront]

LOOK WHAT I FOUND TODAY.

XJ1100 Maxim, XS1100 LG/LH '80-'81, XS1100 SF/SG/SH Specials........ THIS KIT DOES Both Petcocks and fuel cut-off...# 5100

$29.95