petcock diaphragm block hole, rebuild question...

[Bonz]

When putting petcocks back together while rebuilding (from an 80G), there is a hole in the diaphragm block, but it is just a hole, not a hole/passage combo like is shown in the yamaha carb rebuild pictorial link I've been using as a guide

As well, the back of my petcock body has a hole in it that lines up with the hole in the diaphragm block if I put the block in that way.

Do I line these holes up, or do I put the diaphragm block in so the hole is "down and to the rear" like the pictorial shows?

Basically, any thoughts on how the hole in the diaphragm block should be oriented is what I am looking for.

Thanks in advance!

[CaptonZap]

HH,

If I remember correctly, that is a drain hole to get rid of any leakage through the diaphram. So down would be a good place, and if that is to the rear, so be it.

So, having recieved your salt ration, you can now wait for more knowledgeable members to answer.
CZ

[Bonz]

Next question... there is a single hole on each diaphragm membrane. Does that line up with the hole in the petcock body or the hole in the diaphragm block?

[CaptonZap]

Next question... there is a single hole on each diaphragm membrane. Does that line up with the hole in the petcock body or the hole in the diaphragm block?

I think they all line up, but don't quote me.

OK, you forced me into it. After disassembling my spare right side petcock, (PC), here are my findings.
The PC body has a small hole on the diaphram mounting flange that goes to atmosphere. When looking at the up right PC from the back side, the small hole is at the 10 o'clock position. (This is looking at the R side PC. The left might be a mirror image?) The INNER only diaphragm has a small hole that will line up with that hole. The plastic spacer block has a small hole in it that will align with the diaphragm hole. The plastic spacer has a 1/16 in recess on one side, that the little hole connects with. The recess faces towards the center of the bike, when the petcock is installed, with the small holes in the PC body, diaphragm, and plastic spacer all aligned.
Then the outer cover, with the vacuum spigot on it, goes on with the spigot facing forward.
Note that the outer cover has an R or L cast into it, although I don't think that is a critical distinction. It looks as though either R or L would work in either position, but what the hell, might as well do it right, huh?
Don't forget the spring that goes between the diaphram assembly and the outer cover.
So the theory is that if the inner diaphragm springs a leak, the outer diaphragm keeps the vacuum hose from sucking raw gas, the PC still operates normally as far as fuel flow goes, and the petcock dripping would alert the operator to find out WTF.
That's my story, and I'm sticking with it.
Later, CZ

[skids]

I think they all line up, but don't quote me.

Note that the outer cover has an R or L cast into it, although I don't think that is a critical distinction. It looks as though either R or L would work in either position, but what the hell, might as well do it right, huh?
That's my story, and I'm sticking with it.
Later, CZ

Oh yea it matters. If you put the wrong side handle on the petcock, you have to turn the handle straight up for the run position. It did it once.

[skids]

After re-reading the post I guess you were talking about the cover, not the valve handle.

[Bonz]

I am freakin' baffled now... The petcocks are back on the tank, and in the "on" position, hold back the flow of fuel just fine. Grinning happily to myself, thinking the bike might get out for it's first ride after being rehab'd...

So, I start the bike (primed the carbs, so they already have fuel in them) and as soon as it fires up (vacuum lines attached to petcocks), fuel is coming out the hole on the back of each petcock body and no fuel makes it into the fuel ine.

Shut off the bike, and the fuel flow stops right fine.

For grins (not really grinning at this point actually...) I turn it to prime, and fuel comes out each petcock from the same hole, however some does go into the fuel line.

Reserve has the same effect as "on", fuel comes out the hole on the backside of the petcock body with nothing making it into the line.

I've verified I have the levers on the correct side, pretty much double checked everything at least 4 times...

Opinions?

[CaptonZap]

HH

OK, here is what you should check.
Take off the back cover, remove the diaphragms and spacer block, and reinstall thusly.
The diaphragm assembly should have two diaphragms, the inner one, the one that goes onto the petcock flange first, should have a hole that aligns with the hole in the PC body.
The plastic plate has one flat side, and the other side has a circular recess, and a little hole that aligns with the hole in the inner diaphragm. The flat side of the plastic goes against the inner diaphragm, with the little holes aligned.
Next, the outer diaphragm goes against the side of the plastic plate that has the recess in it. There should BE NO HOLES in the outer diaphragm. When the cover is put on, that is the chamber that the vacuum sucks on, to open the valve. If it leaks, the valve will not operate as designed, or not at all, depending on the severity of the leak.
The middle chamber, the one on the side of the plastic plate that has the recess, is there to provide a place for any leakage through the inner diaphragm to collect, and flow out the little hole in the plastic plate, and then through the little hole in the PC flange.
The fuel cannot flow out of the tank until the outer diaphragm is sucked out, opening the fuel port. At that point. there is fuel on the innermost side of the inner diaphragm, and if it is sealed to the flange properly by the plastic plate, there is no way for the fuel to get to the little drain hole without going THROUGH the inner diaphragm to the chamber formed by the recess in the outer side of the plastic plate. Then it drains through the little hole. As soon as the vacuum stops, the valve spring closes the valve, and the flow stops.
Check the inner diaphragm for leaks, especially around the center post.
The fuel porting in the prime position bypasses the vacuum controlled valve, and allows fuel to run around the diaphragm controlled valve and on to the carb. The fact that some of the fuel backs up and comes out of the little hole, after the float valves stop flow to the carbs, means that there is a leak in the inner diaphragm.

The up side is that you got the little holes lined up, other wise it wouldn't drain.

Let us know what you find. CZ

p.s. That may be a work around. Turn the inner diaphragm 90 deg, so that the little hole no longer aligns, put it back together, and you are good to go until the outer diaphragm springs a leak. At which point you will start sucking gas through the vacuum hoses, and your mixture will get real rich on #2&3 cylinders.
I would consider that a "Just to get me home" fix.

[Bonz]

I have to believe the new diaphragms may be defective in some way. Got them from Parts n More as part of their kit. The material is much less robust than the stockers. As well, do I recall reading some diaphragm center posts are shorter than they should be in some replacement kits?

[Bonz]

CZ-

I took the diaphragm assemblies apart, double checked everything, and put it back together. I did find i had plastic block reversed, now it flows like a sieve in the "on" position as well from both 'cocks... Hell, doing it right made it worse. WTF am i missing???....

[CaptonZap]

HH,

Sure sounds like the inner diaphragm is leaking. New?

Were the old ones leaking? Put them back in and see what happens. If the old diaphragms were good, switch the O-rings in the valve stems and see if they work.

You should not be able to twist the inner diaphragm in relationship to the stem, or outer diaphragm. Is it tight between the plates on the stem?

CZ

[skids]

I don't have a spare petcock to look at, but a vaguely remember that mine had hole in both diaphragm sheets. One was turned differently than the allignment of the other holes. Maybe they just punch them out all the same but install them differently so that the breather hole is blocked... I can remember that I had to allign wear marks to get them reinstalled because I didn't know about the holes ahead of time.

[Schming]

Maybe these will help ya:

Right Side Petcock '80G :





















LMK if ya need any more

[Bonz]

I'm really stumped with why my petcocks are not responding to a simple rebuild...

Best I can tell, the diaphragms are not working properly and probably have a micro hole or tear in them by now with all the taking apart and putting back together.

Parts n More gave a partial refund of the cost of the kits, which will allow me to pick up a couple diaphragms from another source.

The diaphragm material in the Parts n More kit were really thin compared to the stockers.

Is there a source that has a more robust diaphragm material, I would like to hear some opinions.

I hear K&L talked about alot, are they a good option vs whatever Parts n More had in their kit? I can find K&L on ebay easily. Does Georgefix use K&L for his kits? I can order them from him as well as he lists them individually.

Thanks.

[jetmechmarty]

Howard,

See if what you need is here.
http://find.partzilla.com/?q=*:*&s=1...%26l+supply%22