Do I have a Dodgy Petcock?

[8Track]

Hi Guys,

When I changed the air filter in the Valk I picked up quite a bit more power, especially roll on at half throttle and above. In the last couple of days this extra power had disappeared again.

I am wondering if its a fuel delivery issue. When I took the fuel tank off to change the air filter I disconnected the fuel line from the petcock, the vacuum hose to No. 6 intake manifold from the petcock, and also the tank vent line.

I am thinking the petcock may not be working properly. I understand the vacuum line is what opens an internal diaphragm to allow fuel to flow. When the vacuum is not there, the diaphragm is supposed to close to stop the possibility of hydrolock if you leave the fuel tap on. I am wondering if the diaphragm is not opening and closing properly due to it either being a bit sticky or the vacuum not being as strong as it should be. Perhaps when I took everything apart and put it back together the diaphragm started behaving correctly, but after some use its back to its old behaviour?

Interestingly I filled up yesterday and turned the fuel tap off. I forgot to turn it back on but still rode all the way home (15kms) without running out of fuel. This tells me the diaphragm must be sticking in a partially open state, delivering enough fuel for normal operation, but not enough for wide throttle openings.

How do I diagnose to find the problem? I guess first would be to inspect the vacuum line for blockages or splits. If that’s ok, what next? would I need to take the petcock apart? If so should I get a rebuild kit for it?

I like to keep my bike completely stock, so not interested in changing to a Pingle

BTW I know the tank vent line is attached correctly and not kinked.

Thanks for your learned advice!

Mark

[Dorkman]

Looks to me that you've zeroed in on the problem already.  The fact that you rode all the way home with a "closed" petcock tells the tale.  I never got a quarter mile with a closed petcock.  I would do the kit and replace the vacuum line, and recheck any other items that were disconnected.

[Bone]

Did you check your tank for rust / scale when it was off the bike ?
It's also a good time to check the screen in the tank.

Riding all the way could be telling you crud is stopping the ball from
sealing when the lever is turned to off and gas is leaking past the ball.

[Chrisj CMA]

My advise to you if you prefer the OEM petcock....Buy a brand new one, dont bother trying to rebuild that old one.  The cover set does ok, but once these things start wearing out, they usually will mess up again fairly quickly. 

[TJ]

    

My advise to you if you prefer the OEM petcock....Buy a brand new one, dont bother trying to rebuild that old one.  The cover set does ok, but once these things start wearing out, they usually will mess up again fairly quickly. 

[Jess from VA]

Only if I drink too much. 

[8Track]

Thanks for the advice guys.

The tank is very clean. There is no rust visible when I look down the fuel filler. I think I will start witha petcock rebuild kit and see how it goes.

Cheers,

Mark

[8Track]

I changed my mind and bought a whole new petcock assembly. Its on its way to Australia from New York and should be here next week. Will post an update once its fitted and tested.

Cheers,

Mark

[8Track]

The new petcock has arrived. Before fitting it I had a closer inspection of the vacuum lines. I found there was a split in the line from No.6 to the petcock! It pays to wear your glasses......

Anyway For now I have simply replaced that vacuum line. Will take the bike out for a run in the morning so will see if this has cured things.

Will report my progress tomorrow.

Cheers,

Mark

[Chiefy]

Good luck on the ride.

[valkyriemc]

My advise to you if you prefer the OEM petcock....Buy a brand new one, dont bother trying to rebuild that old one.  The cover set does ok, but once these things start wearing out, they usually will mess up again fairly quickly.  

Yep, listen to Chris. You can keep messing with the original (I went through the original a new replacement unit) but IMHO you will be re-inventing the wheel. I think most folks would like to keep the bike original but you really need the reliability of an after market unit. I pined my round chrome fascia cover set and knob, so it looks just like it always did. But underneath I have the pingle. G/L

[R J]

You said you found a cracjk in the line later.

Question, if you have not desmogged the bike, then I'd suggest you replace all those little rubber hoses under the tank and above the engine.

Since you want to stay with stock stuff, then I'll not suggest the good hose I put on MGM a few years back.    NO, it is not rubber.

[snakemeister]

 I bought and installed a new OEM petcock for my '97 Tourer . I bought it from @2Wheel Pros for $117.95 freight and all.

[8Track]

Success! The simple act of replacing the petcock vacuum line has cured my roll on acceleration problem.

I took the Valk out for a long ride with a group of café racers through the Adelaide Hills today and found the more I twisted the throttle, the more she gave me! No starvation at all, and I am getting better fuel economy to boot!

So that brand new petcock will stay in the parts stash until its needed.

I will double check all the other smog lines and replace any that look suspect.

Cheers,

Mark

[Chrisj CMA]

If the #6 to the petcock was cracked there is a real good chance the two going to the center intakes are too.  once those have a significant vacuum leak you will have decel popping that you wont be able to clear except by replacing those two lines.  Also check all the nipple caps for the unused intake ports

[8Track]

Thanks Chris,

I will check it all out over the Xmas break.

Regards,

Mark