TOPIC:

My bike has a vacuum petcock (I have no experience with these) that isn't working. It has three settings RES, ON, and PRI (prime). The carbs only get fuel in RES or PRI, it will eventually starve in the ON position. So I have a couple of questions.

1.Is the diaphram just stuck, can it be fixed by cleaning it? If I need a kit wich type/supplier is best?

2.IS PRI drawing fuel higher up in the tank than RES setting? I don't want to find out the hard way.

Prime draws fuel from the reserve port, without the vacuum actuation. RES and ON both need engine vacuum to operate. . .

I think I have my facts straight here. . .I have one of these things and I regularly have trouble with it. . .

Because you indicate your RES works, I would guess your vacuum system is probably working.

I think it was Patton that indicated somewhere in this great big board that sometime rust particles get past the in-tank screen and lodge into the main fuel feed. I think that is what is happened with my bike partially, due to it's aggravating habit of starving for fuel at inappropriate mileage intervals.

Take it out of the tank, pull the screen, and maybe you can flush out the standpipe. . .that is what I plan on doing later today. . .

Hope it works for you and me. . .

KaZooCruiser wrote:

Prime draws fuel from the reserve port, without the vacuum actuation. RES and ON both need engine vacuum to operate. . .

I think I have my facts straight here. . .I have one of these things and I regularly have trouble with it. . .

Wired George is the *goto* guy on this, but...

I've got one of those critters as well.

I'm thinking the RES and PRI settings are both direct feeds, with ON being the vacuum-active.

I had a similar situation to Tyler's on mine a few years back, and on disassembly, found that the diaphram had dry-rotted over the years and split, not allowing the diaphram to open fully once vacuum was applied.

That'd cause the symptoms he's noticed.

Looks like a good excuse to pull the petcock and do a re-build kit, which will handle the standpipe/junk in the manifold issues as well.

ADDENDUM:

Another trick I learned first hand upon doing a petcock rebuild was if the kit doesn't come with a new spring (can't recall who's does) - before re-installing the original spring, it helps to give it a little stretch - not much - before re-installing.

That'll head off a pretty common issue people bring up - rebuild a petcock, and it still weeps gas sitting in "ON".

The reason is that the spring forces the diaphram closed when the motor's off, and like anything else, the original screen gets weaker over time and doesn't apply quite as much pressure.

Post edited by: Pterosaur, at: 2007/04/14 15:24

Thanks all, where is a good place ot get a kit?

Decisions, decisions. . .



Even MORE decisions. . .



Post edited by: KaZooCruiser, at: 2007/04/16 18:57