80G petcock question

[GLoweVA]

I'm gonna ask a silly question here, so please don't laugh at me.
The labels are warn off on my petcocks, so I don't know which positions are which.
Normally I leave them in the vertical position (handle down) and then when it starts running dry, I go to horizontal handle toward the front of the bike.
What positions are there? On / Prime / Reserve ?
There are vacuum lines that hook to the carb ports and these should 'pull'/'suck' open the petcocks when the engine is running.
I've been reading this forum for months now and still don't have a clue about the 80G petcocks. I even took them apart 3 years ago to clean them and still don't have any ideas as to what positions there is supposed to be.
I'm asking because whenever I take the tank off, I have a problem with them leaking a little and not shutting off like I think they should.
Should I get a rebuild kit? If the internal comonents aren't bad, could I just bend the flex washer a little more to give it that little more push to shut it off with no vacuum?
Help please.

[crazy steve]

Yes, you have the three positions (on, reserve, prime). If you modify them by grinding away the little 'stop' on the chrome faceplate, you can add a 'off' (lever pointing up).

If they're leaking, they probably need to be rebuilt with new seals and shut-off diaphram. Increasing tension on the wave washer won't help...

[GLoweVA]

So what's the difference between on and prime ? and which positions are they?
As far as the leaking thing, could the internal parts need some lubrication?
3 years ago when I had them apart, I noticed that it was VERY snug in there and they were/are tight to move.

If I had them in the on position, then they wouldn't shut off and that may be the cause of my 'leaking'.

[CatatonicBug]

In the "ON" position, the fuel only flows when the engine is running, and vacuum pressure is applied from the engine. The "Prime" position allows fuel to flow without the engine running. "reserve" is just like "ON", but pulls fuel from the lower part of the tank (2-stage filter tower on top of the petcock in the tank), allowing you to "run out" of fuel, but still have enough to get you to a gas station.


Using the "reserve" position on a regular basis opens you up to the possibility of ingesting the tiny sludge pieces that settle in the bottom of the fuel tank, but are too small to be filtered out by the built-in petcock fuel filter. This is the main reason for adding in-line fuel filters to the circuit.

Mine is a Special, so I also have an "Off" position, so I'm not sure where the actual positions are located on the Standard petcocks. As Steve said, if your petcocks don't shut the fuel off in the "on" position, with the engine NOT running, your petcocks need to be rebuilt.

[crazy steve]

The 'fuel on/fuel off' part of the standard petcock is done by the vacuum diaphram on the back of the petcock and is automatic; motor running fuel flow, stopped no flow (which is why there's no 'off' position). The prime position bypasses the diaphram and allows fuel flow whether the motor is running or not.

Lever positions are: pointing forward is reserve, down is on, and towards the rear is prime.

The only thing you can lube is the outer o-ring on the lever. If you're getting leaking when the petcocks are in the 'on' or 'reserve' position with the tank off the bike, the vacuum diaphram isn't sealing. There's a small o-ring that you may be able to replace if you can find one, but otherwise you'll need a rebuild kit. DO check for internal corrosion when the petcock is disassembled, because if the seat for that o-ring is damaged, you'll have to either replace the petcock or convert it so it has a 'off'.

[GLoweVA]

Thanks Steve and Cataonic. That was exactly what I was looking for. I didn't know where the prime position was or the difference between it and 'on', now I do. Time to take the tank off again and pull the petcocks and commence to 'fixing' them.

After that is done, time to pull the carbs and find and fix the 'fuel out of the airbox' issue. I figure a triple clean, float height check (with the sight tube and float valve leak check) should do it.
Then a compression check to make sure that everything is ok on the head.
Bench sync, then put it all together and go from there.

Every time I think about getting a new bike, I say to myself, Why? this is so much fun! (well, only when things go right and everything gets fixed)

[cywelchjr]

Thanks Steve and Cataonic. That was exactly what I was looking for. I didn't know where the prime position was or the difference between it and 'on', now I do. Time to take the tank off again and pull the petcocks and commence to 'fixing' them.

After that is done, time to pull the carbs and find and fix the 'fuel out of the airbox' issue. I figure a triple clean, float height check (with the sight tube and float valve leak check) should do it.
Then a compression check to make sure that everything is ok on the head.
Bench sync, then put it all together and go from there.

Every time I think about getting a new bike, I say to myself, Why? this is so much fun! (well, only when things go right and everything gets fixed)

Fuel out of the airbox on a 80G if the carbs have not had a full rebuild with complete kits is very likely the o-ring on the float needle valve. You don't need to replace other parts unless the needle valve viton tip has gotten damaged over time, but that o-ring flattens out and needs replaced after 30 years. The correct size o-ring comes in the viton o-ring kit from harbor freight, IIRC there are 10 of them in there. Also, before you put them back together, make sure to adjust BOTH tabs, both the one for height, and for float drop (yes there is an adjustment for how far they can drop) cause if they drop too far the needle valve can get cocked in the seat and you have to tap on the carbs to get them to seat, this adjustment will prevent that, the floats only need to be able to drop about 1/4 to 1/2" to allow all the fuel flow the engine can consume at full throttle and redline.

[GLoweVA]

Thanks for that tip about the other tab. I read it somewhere here last week.
Last month when I had the carbs out and adjusted the floats, I didn't know about the other tab and that may be my problem.

Oh yeah, I gotta change the oil too, just in case there's any gas in there.
Then I can fire it up and tune and tweak and check plugs etc.

[Ken Talbot]

Inside the standard petcocks, there is an odd sort of one-way valve that maintains a bit of vacuum for a while on the dry side of the diaphragm when the engine stops. I'm not sure how long this is supposed to last, but there is a very small pressure relief hole very similar to the small orifice in a master cylinder.

When this bleed off hole gets plugged, the vacuum against the diaphragm is maintained for quite a while, much longer that I like. If you're bench testing your tank and petcocks, it will look like the diaphragm is not working properly at all.

My solution to this has been to get in to where this bleed-off control is, which I like to call the petcock spooge hole, and ream it open with a decent size drill bit. Now, the second the vacuum against the diaphragm is shut off, my petcocks all snap immediately and fully shut. When I bench test them at the start of each season, they work the way I like them to, with not a drop of fuel dribbling out once the vacuum is gone.

YMMV

[cywelchjr]

Inside the standard petcocks, there is an odd sort of one-way valve that maintains a bit of vacuum for a while on the dry side of the diaphragm when the engine stops. I'm not sure how long this is supposed to last, but there is a very small pressure relief hole very similar to the small orifice in a master cylinder.

When this bleed off hole gets plugged, the vacuum against the diaphragm is maintained for quite a while, much longer that I like. If you're bench testing your tank and petcocks, it will look like the diaphragm is not working properly at all.

My solution to this has been to get in to where this bleed-off control is, which I like to call the petcock spooge hole, and ream it open with a decent size drill bit. Now, the second the vacuum against the diaphragm is shut off, my petcocks all snap immediately and fully shut. When I bench test them at the start of each season, they work the way I like them to, with not a drop of fuel dribbling out once the vacuum is gone.

YMMV

I don't know what it's called in there. But in the piano world in the player piano's where a device almost identical is used it's called a vacuum bleed and that's exactly what it's for, and I'm guessing that corrosion makes the hole close up some. I wouldn't use a drill bit as it's purpose is to prevent excessive working of the diaphragm, so as to keep it from wearing out too quickly, so I would use a small wire to make sure it's not clogged at all. And if you want it off right now, blow into the hose . I think that like the orifice in the vacuum advance line, it's supposed to let the vacuum build up and stay up and not have that little valve opening and closing with each stroke of the cylinder.

[CaptonZap]

One other thing, the positions of the lever are engraved, (stamped) on the petcock covers. When you take them off, you might look on the back side and see if the inattentive PO put them on backward.

(Isn't it great to have the PO to blame for all the problems?)

CZ

[Ken Talbot]

in the piano world in the player piano's where a device almost identical is used it's called a vacuum bleed and that's exactly what it's for

It never ceases to amaze me the kinds of stuff people here at the forum know. Who would have thought there would be someone who knows about both XS11s and player pianos! And now that you mention it, vacuum bleed sounds like the perfect thing to call that little device in the petcocks.

May not be as catchy as petcock spooge hole, but I like it. Now let's see if I can remember it next time it comes up.

So, anything else in common between an XS and a player piano?

[cywelchjr]

It never ceases to amaze me the kinds of stuff people here at the forum know. Who would have thought there would be someone who knows about both XS11s and player pianos! And now that you mention it, vacuum bleed sounds like the perfect thing to call that little device in the petcocks.

May not be as catchy as petcock spooge hole, but I like it. Now let's see if I can remember it next time it comes up.

So, anything else in common between an XS and a player piano?

They both make wonderful mechanically produced music .

[GLoweVA]

Wow, Vacuum bleed hole. I would have never thought to look for that. Hind sight being 20/20, It makes perfect sense that there would be a hole to bleed off the vacuum and alow the thing to go shut.
Depending on how small the hole is, I might use a VERY small drill bit to clear it out. Mine do have a little bit of corrosion on them.
As far as the label plate, I'll check the backside, but the last time I had them out, I don't remember seeing anything on either side, but I'll check. Maybe I'll use a sharpie to label them, LOL!

[cywelchjr]

It would be pretty hard to get rid of the labels, IIRC they are stamped into the cover pieces. One would have to sand them down to get rid of them, or replace them with something else that didn't have them, so if the marks are not showing it would be most likely that they are turned around so you can't see them.