Fuel Flow Issue?

[sdv003]

I was riding from Denver to Las Vegas the other day when this issue cropped up.  At about half a tank, the girl was starting to bog like see needed to be switched to reserve.  When I switched to reserve, she came back strong.  I switched back to the main tank and it was ok for another 10 minutes or so, then the process had to be repeated.  It went away when I filled the tank, until the tank was approx half full again.  It only occurred when I was driving in the hot desert (105*F+) and at 75mph or better.

My speculation is that when it's that hot, perhaps the fuel is starting to form bubbles.  By switching to reserve, I get a bit more head pressure on the fuel line which removes the bubbles for a while.  I will admit to using one of the redeye quick disconnects, but I've never had a problem before with it.  I've never experienced it on my regular commute, where it has been at least as hot and the tank level much lower, thought the speeds aren't as high.

It was more annoying than anything else, but I'd like to get it dealt with.  Any thoughts on what might be happening are appreciated.

[Roidfingers]

Had a problem with my redeye qd. Just tossed in trash. Didn't work for me either. And its just as bad or worse to connect then original.

[The emperor has no clothes]

I agree it's probably your quick disconnect. But I had the same symptoms once from my fuel selector not turning open all the way. It was because of the chrome engine hanger mount. Once that was fixed its been fine.

[N8171S]

I just returned from Denver where it was nearly 100 degrees and had the same  issue.  The bike ran fine on Pikes peak and Independence pass but the temp was cool.  When I got back to Denver the problem happened again.  Took off the tank and found that the rubber in the petcock had swelled up blocking the flow.  Took all that crap out plugged the vac line and rode back to Massachusetts without any more issues.  I now use the petcock for reserve, on and off only.  Installed a Dan Mark shut off.

[MarkT]

Pretty much identical issue on the ride to/from Inzane, 3200 miles total.  Pulling a heavy trailer, had starvation at higher speeds and once the temp got into the 90's, especially with higher demand like up long hills. Had to keep the tank fairly full to have enough head pressure.  I have a belly tank plumbed as a big reserve while the fuel is delivered same as OEM from the main tank by gravity. Had to send the belly fuel to the main keeping it pretty full. I have a Dan-Marc, smaller orifice 0.152", and a fuel filter provided by R&M (belly tank people) inline on the gravity line.  I have replaced the Dan-Marc with a Ehcotech solenoid, much larger.  Still having the problem.  About to pull the fuel filter.  Have made sure, fuel line is level or downhill, no loops. The first NAPA transparent filter caught some crud from inside the belly tank - looks like welding slag.  Gonna backwash the R&M filter and move it to the delivery line from the belly tank.  Before it had very good flow, compared to the other filter from NAPA. Possibly it could be partially blocked from crud it caught.  My petcock is OEM but modified as manual only. Have not looked for add'l problems in it.

[Chrisj CMA]

I was riding from Denver to Las Vegas the other day when this issue cropped up.  At about half a tank, the girl was starting to bog like see needed to be switched to reserve.  When I switched to reserve, she came back strong.  I switched back to the main tank and it was ok for another 10 minutes or so, then the process had to be repeated.  It went away when I filled the tank, until the tank was approx half full again.  It only occurred when I was driving in the hot desert (105*F+) and at 75mph or better.

My speculation is that when it's that hot, perhaps the fuel is starting to form bubbles.  By switching to reserve, I get a bit more head pressure on the fuel line which removes the bubbles for a while.  I will admit to using one of the redeye quick disconnects, but I've never had a problem before with it.  I've never experienced it on my regular commute, where it has been at least as hot and the tank level much lower, thought the speeds aren't as high.

It was more annoying than anything else, but I'd like to get it dealt with.  Any thoughts on what might be happening are appreciated.

Sounds like the beginning of a petcock failure.  If it is, this fuel flow deficit will get worse and worse until its rebuilt, or better yet replaced with a quality valve.

[sdv003]

Not saying it can't be a petcock failure, but I only have 6K miles on it since I rebuilt the OEM petcock.

[Chrisj CMA]

Not saying it can't be a petcock failure, but I only have 6K miles on it since I rebuilt the OEM petcock.

Yep, my story exactly.  Rebuild, repeat, then replace.  Now I really suspect a petcock failure.

[Patrick]

Kinda sounds as though it may be time for a Pingle and throwing the disconnect in the trash.

[The emperor has no clothes]

Not saying it can't be a petcock failure, but I only have 6K miles on it since I rebuilt the OEM petcock.

Yep, my story exactly.  Rebuild, repeat, then replace.  Now I really suspect a petcock failure.

I've got 160 k on stock petcocks. It's more than likely the quick disconnect. Many have had problems with them.

[Grumpy]

That quick disconnect will leave you stranded, mine quit passing fuel and had to fix it on the road in the smokies.  Tossed it in the trash, never again. Go with a pingle and a dan mark shutoff.

[gordonv]

A fellow ride had the same kind of problem riding last year in the high land deserts (heat and elevation). Seemed to come on at half a tank. Nothing of the usual trials made it go away, other than toping the tank.

Had also happened another couple of times over the year. I haven't heard how me made out on his month long ride this year.

He never had the tank off. Opened the tank. Tried the petcock.

He thought it might have been bad fuel (might have been, I think his bro had some sputtering also).

[Mr.BubblesVRCCDS0008]

Both my valks have done it from time to time in really hot south Texas weather. I'm running stock petcocks with the vacuum side gutted and are now a manually operated valve. never really been a problem. Did have one vaporlock once sitting in traffic in 100 degree+ weather. The tank was low on fuel and  the bike started to die and as I tried to gas it the valves started rattling scared the hell out of me. Got to the side of the road killed it and let it cool while traffic cleared, fired it up and all was good.

[Willow]

Those are the precise symptoms of a bubble in the fuel line.  That can be caused by a quick disconnect that is not PERFECTLY level or by an elongated fuel line.  Sometimes the fuel line gets elongated when someone adds an inline fuel filter.

The Valkyrie fuel system cannot tolerate any uphill portion of the fuel line.  The uphill bump, even slightly, in the fuel line will result in an air bubble that causes it to behave very much as if it's running out of fuel.  Oftentimes a switch to reserve will, as you've noted, bring on enough pressure to cause the symptoms to go away.  It does seem to happen more frequently in the heat.

I'd bet you big bucks there is nothing wrong with your petcock.       

[MarkT]

Did what I said above.  Now Dan-Marc 0.25" orifice #121 solenoid.  Moved the fuel filter to the belly tank pump line. Pretty certain no uphill segments on the gravity line, main tank to carbs. Petcock is manual only.  If it still has the problem - gotta look at the petcock.  Don't want to go to Pingle - want to retain the easy reach as I switch to reserve frequently while managing the fuel tanks.

[MarkT]

Something to look at if you "manualized" your OEM petcock. While working on a fuel leak I had opportunity to isolate the petcock and test it separately.  Very low flow out of it no matter the selection.  Took it apart including the riveted side.  Nothing obvious amiss.  I had made it manual-only per R&M's instruction.  They had said put it together minus some parts including leave out the spring. Apparently now the fuel shut-off diaphram had settled against the outflow port and was impeding it to the point of starvation.  The diaphram must be there as it's perimeter acts as an O-ring to stop leakage from between the plates. I installed a right-sized spring to hold the diaphram away from the port.  Flows fuel as it should now.  Why it worked at all - the diaphram must have stayed away from the port for awhile, then shifted. I reviewed R&M's instructions I had followed - yep, I did it as they said. So if you changed your petcock to manual and are having flow problems - look at this.

[Valkorado]

Something to look at if you "manualized" your OEM petcock. While working on a fuel leak I had opportunity to isolate the petcock and test it separately.  Very low flow out of it no matter the selection.  Took it apart including the riveted side.  Nothing obvious amiss.  I had made it manual-only per R&M's instruction.  They had said put it together minus some parts including leave out the spring. Apparently now the fuel shut-off diaphram had settled against the outflow port and was impeding it to the point of starvation.  The diaphram must be there as it's perimeter acts as an O-ring to stop leakage from between the plates. I installed a right-sized spring to hold the diaphram away from the port.  Flows fuel as it should now.  Why it worked at all - the diaphram must have stayed away from the port for awhile, then shifted. I reviewed R&M's instructions I had followed - yep, I did it as they said. So if you changed your petcock to manual and are having flow problems - look at this.

I'll have to watch for this, Mark.  When you say right sized spring did you have to replace the OEM spring?  I had a petcock leak so I did the R&M mod before the NM trip.  This process:

http://valkyrie.smugmug.com/gallery/3097483#169542872
(look for lime green tape measure and about the next dozen photos)

No problems thus far without a spring installed.  I don't have a belly tank, but I do have a Dan-Marc.

[big poppa pump]

Something to look at if you "manualized" your OEM petcock. While working on a fuel leak I had opportunity to isolate the petcock and test it separately.  Very low flow out of it no matter the selection.  Took it apart including the riveted side.  Nothing obvious amiss.  I had made it manual-only per R&M's instruction.  They had said put it together minus some parts including leave out the spring. Apparently now the fuel shut-off diaphram had settled against the outflow port and was impeding it to the point of starvation.  The diaphram must be there as it's perimeter acts as an O-ring to stop leakage from between the plates. I installed a right-sized spring to hold the diaphram away from the port.  Flows fuel as it should now.  Why it worked at all - the diaphram must have stayed away from the port for awhile, then shifted. I reviewed R&M's instructions I had followed - yep, I did it as they said. So if you changed your petcock to manual and are having flow problems - look at this.

This happened to me as soon as I changed my OEM petcock to a manual one and took it out for a test ride. Bike shut down 5 miles away from home and had to get the bike towed back. First thing I did was completely remove the entire innards of the diaphragm and use it purely as an O-ring. I also used Permatex fuel resistant (blue) gasket and sealant between the 2 halves when I put it back together. Been 3 years since I've done this and never given the petcock a second look.

[MarkT]

Something to look at if you "manualized" your OEM petcock. While working on a fuel leak I had opportunity to isolate the petcock and test it separately.  Very low flow out of it no matter the selection.  Took it apart including the riveted side.  Nothing obvious amiss.  I had made it manual-only per R&M's instruction.  They had said put it together minus some parts including leave out the spring. Apparently now the fuel shut-off diaphram had settled against the outflow port and was impeding it to the point of starvation.  The diaphram must be there as it's perimeter acts as an O-ring to stop leakage from between the plates. I installed a right-sized spring to hold the diaphram away from the port.  Flows fuel as it should now.  Why it worked at all - the diaphram must have stayed away from the port for awhile, then shifted. I reviewed R&M's instructions I had followed - yep, I did it as they said. So if you changed your petcock to manual and are having flow problems - look at this.

This happened to me as soon as I changed my OEM petcock to a manual one and took it out for a test ride. Bike shut down 5 miles away from home and had to get the bike towed back. First thing I did was completely remove the entire innards of the diaphragm and use it purely as an O-ring. I also used Permatex fuel resistant (blue) gasket and sealant between the 2 halves when I put it back together. Been 3 years since I've done this and never given the petcock a second look.

I was about to circumsize the diaphram when I realized that would allow the fuel to run out the vent.  So I put in the spring.  Now I think I might take it out, snip it and put permatex in the vent hole - not needed now that it's manual.  I have that same blue permatex.  And #2, and #3 aviation...

[big poppa pump]

Something to look at if you "manualized" your OEM petcock. While working on a fuel leak I had opportunity to isolate the petcock and test it separately.  Very low flow out of it no matter the selection.  Took it apart including the riveted side.  Nothing obvious amiss.  I had made it manual-only per R&M's instruction.  They had said put it together minus some parts including leave out the spring. Apparently now the fuel shut-off diaphram had settled against the outflow port and was impeding it to the point of starvation.  The diaphram must be there as it's perimeter acts as an O-ring to stop leakage from between the plates. I installed a right-sized spring to hold the diaphram away from the port.  Flows fuel as it should now.  Why it worked at all - the diaphram must have stayed away from the port for awhile, then shifted. I reviewed R&M's instructions I had followed - yep, I did it as they said. So if you changed your petcock to manual and are having flow problems - look at this.

This happened to me as soon as I changed my OEM petcock to a manual one and took it out for a test ride. Bike shut down 5 miles away from home and had to get the bike towed back. First thing I did was completely remove the entire innards of the diaphragm and use it purely as an O-ring. I also used Permatex fuel resistant (blue) gasket and sealant between the 2 halves when I put it back together. Been 3 years since I've done this and never given the petcock a second look.

I was about to circumsize the diaphram when I realized that would allow the fuel to run out the vent.  So I put in the spring.  Now I think I might take it out, snip it and put permatex in the vent hole - not needed now that it's manual.  I have that same blue permatex.  And #2, and #3 aviation...

Plug the vent and the weep-hole with JB Weld, not Permatex. Use Permatex around the border to seal the 2 halves and you should be good.