Question on fuel tap assy. ..

[thewiz]

While rebuilding the fuel taps on my F today, I noticed that on the right side tap, within the vacuum diaphram cap there is a brass plug or restrictor that appears to be peened in place. That petcock works fairly well but not what I'd consider perfectly, even after renewing the seals and such.

When I took apart the left side, that brass plug fell out on the bench along with a small rubber washer. That brass plug appeared to be peened in at only one point and obviously it hadn't held. The other side had three peen points around the plug and it wouldn't come out at all. I put it back togther with the washer under the plug and peened a tiny bit of metal to hold it in place and it doesn't work well after the rebuild either ... continually dripping slightly ... a drop here and there ... Nuts !

The question is: Does that brass plug belong to be crimped into the vac. cap and does that washer go under the plug and next to the cap or what? There was no rubber washer evident in the right side at all ... so maybe it's underneath or just missing? Dunno. I have four different manuals and none show this figure well enough. There are 11 pages of 'fuel petcock' threads ... Anyone know?

[GARTHXS]

me too

Yeah , Wiz I saw the same thing when I popped mine open , it looks like a valve of some sort

[dbeardslee]

Wiz - The rebuild kits I've seen don't include new springs. When I rebuilt mine I put some stiffer diaphram springs in, and bent the big round spring that sits under the lever a little more. Had 'em working great for a while and then they started leaking again. Finally s-canned 'em and replaced with manual petcocks from partsnmore. Have to turn 'em on and off but they work much better.

[GARTHXS]

vacuum side

He's talking about the other side of the taps when you pull off the side with the diaphrams there is a port with a brass insert in between the vacuum inlet and the inside of the fuel tap

[randy]

That little brass doohickey is a restrictor. It helps reduce the oscillation of the diaphram under engine vacuum. Probably extends the life of the diaphram.

[dbeardslee]

Garth - He was also talking about a leak. The little brass thing won't make it leak, but the springs will.

[thewiz]

Right on, D and Randy ..

What I'm trying to learn is:

Should that brass thingy be peened in place with the rubber washer underneath it ... or some other way? The brass restrictor (now I know what it is anyway ) fell out in my hand along with this little washer exactly the same diameter. Doesn't seem like anyone's really had one of these apart.

Good idea on the springs too ... think I'll give 'em a little stretch... like all the other 30yr old springs that have been compressed for that amount of time, they've probably gotten shorter and weaker.

[dbeardslee]

I don't think it makes much difference. I had the same situation on mine, and after you and Garth's experience I'm starting to think it's relatively common. When I put mine back together I just put the brass thing in its hole and closed it up. Like I said, it worked fine for a while and then started leaking again. Another very experienced XSive warned me before rebuilding the petcocks that he had had varied results with rebuilds. Has something to do with the oxidation of the metal and the tolerances getting loose.

[Ken Talbot]

Petcock spooge hole

Inside that brass bit is a sort of a flapper valve. When there is vacuum in the vacuum hose, it gets pulled over from its brass seat, which allows vacuum against the diaphragm, which permits fuel flow through the petcock. When the engine stops and there is no more vacuum in the hose, the flapper moves back against the brass seat, and a small hole in the middle of the flapper bleeds off the vacuum, which eventually allows the spring to push the diaphragm over to shut off the fuel flow. Yes, this means the petcock will keep dribbling or flowing fuel for while even with no vacuum. If that hole is plugged, the vacuum never gets released, fuel continues to flow, and if your float valves are also not working properly, you get a crankcase of fuel.

In my mind, this qualifies this hole to be called the petcock spooge hole. And yes, it is a cousin of the spooge hole in the bottom of the float bowls, and the spooge hole in each of the master cylinders. They're all small, they all plug up, thay can all be hard to find, and they all cause an inordinate amount of grief for a new XS owner. I make that 8 spooge holes on a Standard, and 7 on a Special. For the bonus points, why does the Special have one less?

On all of my Standards, I have taken a bit of wire a bit larger than this spooge hole and reamed it out to make sure it is clear, and is large enough is is not going to plug again. Now, when I release the vacuum from the line, the diaphragm snaps over immediately and I know I'm not going to have a leak.

[DGXSER]

Ohhhh....Ohhhh.....Ohhhh.....Ohhh......

(In my best Horseshack voice)....Cause the special would only have one vacuum valve for fuel, the Octy, and none in the petcocks. Thats my story and I'm stickin to it....at least until I sit corrected again.

I always need all the bonus points so I can bring my grade up to passing.

[Ken Talbot]

You got it, DGXSER! That little problem causes so many octopi to leak, and so many Special owners to toss it out and go back turning their petcocks off and on by hand. It's really not that hard to fix

Any time you want to swing by the house you can collect your prize!

[Ivan]

Darn, I was going to say that specials have one less because they are "Special".

I too agree that the vacuum valve on the specials is an easy fix. I fixed mine without using a kit. just some fuel proof sealant and a fifteen cent oring.

[DGXSER]

Substitute a scalpel for your eyes.....

that is why mine is off now. When I got the bike my octy was not working, so I decided to open it up and have a look see. Now it leaks. When reviewing everything I noticed a kink mark in the vacuum line from the boot to the octy. Guess why it was not working? Yep, so I now have a leaker that got in the way and sits on my work bench. Another someday project.

[thewiz]

Very interesting, Mr. Talbot ..

I don't think have enough cogintive reasoning skills to actually figure that out on my own. That is a very cool explanation of that simple mechanism. Thank you, Ken.

Yes, this means the petcock will keep dribbling or flowing fuel for while even with no vacuum

Are you saying that: even when working properly, when vaccuum is released, some drippage will occur anyway? Cuz I'm only dealing with a drop every so often when vacuum is released ... not the outrush of fuel that happens when vacuum is applied .... or anything close to that.

[Ken Talbot]

Yes, the petcocks will drip for a little while, until the vacuum is released from the chamber next to the diaphragm. And the more that wee orifice is blocked, the longer the vacuum will last and the longer it will keep dripping.

I prefer to basically destroy that flapper bit so I can be sure the fuel flow stops as soon as the motor stops. I test this all with the tank off the bike, sitting on a small sheet of plywood across a couple of saw horses. I suck on a vacuum hose connected to the vacuum nipple of the petcock to ensure the fuel flows freely into a container. As soon as I stop sucking, I expect the flow to stop completely and instantly. If it doesn't, I take the petcock off to make sure the orifice is clear, the spring is providing adequate pressure, and the o-ring that actually stops the flow is in good condition.

O-rings are cheap to replace, and it is easy to pull the spring out to stiffen it up. I'm pretty sure my float valves are in good working condition so they would stop the fuel flow anyways. But, I still like the added insurance of knowing my petcocks are working too.