Fueling issues after Pingle conversion

[Kurlon]

My first weekend at the track on my GS500, I ran into fuel flow problems.  Once I hit about half a tank, the bike wouldn't flow gas reliably.  As long as I kept it over half a tank, I was ok.

Prior to that weekend I put on a keyless gas cap, and removed the vacuum operated petcock system and installed a Pingle petcock on the tank that goes to a quick disconnect, and then the carbs.  The stock system is notorious for starving the carbs for fuel on street bikes, and just generally failing without warning, plus I didn't like the idea of an octopus of hoses on a race bike when all that's needed is one line.

When the problem occurs, you can see just a trickle of gas flowing down the line, with the line only partially filled.  Switching to reserve didn't seem to help.  Wait long enough, and the trickle will fill the bowls and allow me to continue till the next time I go WFO. My first thought was tank venting, but removing the gas cap doesn't alter the flow.

I've finally healed to the point that I can start wrenching on the bike again, and decided to check things out today.  I undid the fuel line from the carb, left the quick disconnect in the line, dropped it into a gas can, and opened the petcock.  Starting with a full tank, it flowed good and strong, for the first 1.5 gallons or so, and then stopped.  I removed the gas cap, no change.  Switching to reserve resumed the flow, only now I can see bubbles in the line.  At about the 2 gallon mark the tank was 'breathing' even with the cap off. It'd be quiet with good flow, the flow would slow and the line would fill with bubbles until there was mostly air in the line, which would then rush out the petcock into the tank audibly, restarting flow.

I know I don't have a tank venting issue, I've got a 1" hole in the top where the cap goes right now and it's still doing it.  What's causing this 'breathing' behavior?  (And better still, how do I fix it?)

[ben2go]

Did you have to grind the hole open to fit the new petcock?Has the tank ever been lined?Sound like there is some lining material floating around and getting sucked against the inside part of the petcock,blocking the fuel flow.Also do the disconnects have a 1 way valve built in to stop flow when they're disconnected.Some have this feature and will stop working correctly at low flow(low fuel levels).Where did you get the disconnects?Link if you have it.

[Kurlon]

Yes, I did have to file the hole into the tank larger for the new petcock.

The tank has not been lined, and much to my surprise, for a 91 it's still very clean inside, no rust that I can spot.  I pulled the petcock out yesterday to inspect it while testing, and couldn't find any debris, etc on it.

The quick disconnect is a 'motion pro' unit; http://www.motionpro.com/motorcycle/partno/12-0030
It eats o-rings like candy so I'm likely going to ditch it.  It's too bad, it makes removing the tank MUCH easier.  If I can find one without a check valve that doesn't lunch o-rings as quickly I'll happily switch.  I did all my testing through it, I'll retest without it and see if that makes any difference.

[ben2go]

Yes, I did have to file the hole into the tank larger for the new petcock.

The tank has not been lined, and much to my surprise, for a 91 it's still very clean inside, no rust that I can spot.  I pulled the petcock out yesterday to inspect it while testing, and couldn't find any debris, etc on it.

The quick disconnect is a 'motion pro' unit; http://www.motionpro.com/motorcycle/partno/12-0030
It eats o-rings like candy so I'm likely going to ditch it.  It's too bad, it makes removing the tank MUCH easier.  If I can find one without a check valve that doesn't lunch o-rings as quickly I'll happily switch.  I did all my testing through it, I'll retest without it and see if that makes any difference.

Sounds like a good idea.Philips Lockhart made some disconnects.Not sure if they use the check valve tho.Here is what I use.I got it at Lowe's and it disconnects like an air fitting.With this you turn the valve off and leave the petcock on.I think it was $8.

[jeremy_nash]

maybe you could remove the checkvalve plunger from your quick-disconnect?  of course that would only be any good if removing the disconnect had an effect on your problem

[werase643]

why not remove the quick disconnect and see what happens

don't mean to be a duck but common sense still applies
if it ain't the QD it's the Pingle

[Kurlon]

Update on the GS500E fueling issues...

Tested fuel flow without the quick disconnect, same problem, the moment the tank starts flowing through the reserve orifice in the petcock, it starts up with the poor flow/bubbles in the line/"breathing" routine.  So, the problem is the Pingle petcock.

I cut down the primary feed tube, then reinstalled the filter mesh.  A quick test shows I can now reliably drain the tank down almost completely with a solid reliable flow, fuel cap in place, success!  A quick test jaunt around the parking lot shows I may have partially clogged my pilot jets while the bike sat from April on.  The idle is low once warm and off choke, and the revs hang after a blip of the throttle.  Minor problem, and I've got another weekend to tinker on it.