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Discussion Starter · #1 · (Edited)
03 V500, 23,500 mi

During the 18,000 miles I've ridden this bike, I've (occasionally) experienced the same nagging problem. Under power, always going at least 50mph or faster, the engine will starve for fuel. Switching to reserve doesn't help, no matter if the tank is full, half full or whatever. Switching to prime instead of reserve doesn't help either. The only thing that restores fuel to the engine is pulling over and waiting a few minutes (engine not running) while in the prime position. After again getting underway, sometimes I can switch back to "On" and the bike will run fine, but sometimes I have to leave the petcock in the prime position.

This problem has been reported before by other 500 owners on this forum but no definitive answer as to the cause has been found (I searched).

1. Rebuilt the petcock - experienced the same condition.
2. Replaced petcock with OEM - experiencing the same condition.
3. There is NO "swoosh" noise heard when opening the gas cap, so I'm 99.5% sure the cap vent mechanism is not defective, and both vent lines are clear (also checked).
4. Petcock filters have always been spotless and I've repeatedly cleaned and drained the tank thinking maybe a bit of plastic has been floating around in there - can't find a thing.
5. Main fuel line is not kinked in any way - smooth run from petcock to carb crossover.
6. It is NOT an electrical problem.

When I said it "occasionally" happens that's just what I mean. Very sporadic - sometimes thousands of miles between occurrences, sometimes two days in a row. I'm just stumped and concerned this will happen in a bad traffic situation - I can't ride hugging the right lane all the time.

Sure could use some opinions from you Vulcan 500 gurus.
 

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redfish,

Hidalgo too has been afflicted by this malady. The most recent time was during my and Daniel's IBA Memorial 1000. It happened in heavy 75 mph traffic on I-20 and was a fairly large 'pucker moment' because we were in the left lane with no shoulder and several short bridges. I managed to get us pulled off of the road without disrupting traffic or getting run over. It took a couple of minutes of cranking to get her fired up again and she ran flawlessly for the rest of the ride.

I am sure that the problem is fuel related by the way she acts. This has happened very intermittently during her life and I believe that is related to the tank vent.

Bill
 

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We call it POOGS, phantom out of gas syndrome. Here is a fix for the Vulcan 750.

Subject: Phantom Out Of Gas Syndrome (POOGS)

Symptoms: Motorcycle stalls repeatedly as the fuel level in the gas tank falls below 1/2 full. Symptoms similar to running out of gas. Switching to Reserve has no effect.

Root Cause: Failed gas tank venting system; clogged gas cap vent and/or gas tank vent tube or a failed check valves within the gas cap vent assembly. This prevents air from entering the gas tank to displace fuel being used by the carburetors, resulting in negative gas tank pressure (or vacuum). Negative gas tank pressure prevents fuel from reaching the carburetors causing the motorcycle to stall.

Verification Steps:
Fuel level at 1/2 tank of gas or less.
Ride for a few miles.
Motorcycle stalls as if out of gas.
Pull over in a safe location.
Open gas cap for 3-5 minutes. This relieves the negative gas tank pressure momentarily.
Close gas cap
With a few extra cranks the motorcycle starts like there is no problem
Go to step #2 and symptoms repeat
Solution: Clean gas cap venting system and verify that the gas cap vent assembly check valves are functioning properly. Optional: The gas tank vent tube (’88 – ’06, non-CA models only) exits in front of the rear tire and may be rubbing against the spinning rear tire, resulting in a clog that resembles black carbon. Relocate the gas vent tube exit, if this is determined to be the debris source.

Gas Tank Venting System Cleaning Instructions: The process looks complicated, but it only takes about 15 minutes. NOTE: Instructions below are for ’85 – ’06, non-CA models only. Adjust accordingly for CA (vapor recovery system) models.

Step I: Clean the gas tank vent tube/exit.
For '85-'87 Models with no gas tank vent tube (click on Attachment 3602 for more information):
These models vent through a small port in the base of the gas cap. The port exit is located in the rear of the gas cap (see attachment above for details.)
Open the gas cap.
Locate the gas tank vent port entrance; a small hole located on the gas tank directly in front of the opened gas cap hinge.
Spray carburetor cleaner or non-chlorinated brake cleaner, using the straw attachment, directly into the gas tank port entrance. The cleaner should exit the rear of the gas cap freely. Have a rag handy to prevent cleaner from running down the sides of the gas tank.
Use a pipe cleaner or small plastic zip tie to unblock a clogged port, if necessary.
For '88-'06 Models with gas tank vent tube:
Place a piece of paper in front of the gas tank vent tube exit. The default (OEM) location is directly in front of the rear tire.
Open the gas cap.
Locate the gas tank vent tube entrance; a small hole located on the gas tank directly in front of the opened gas cap hinge.
Spray carburetor cleaner or non-chlorinated brake cleaner, using the straw attachment, directly into the gas tank vent tube entrance until drips are observed on the piece of paper placed at the gas tank vent tube exit.
Continue spraying until the drips run clear.
Step II: Clean the gas cap vent assembly.
Open the gas cap and remove the key.
Cover the tank inlet tube to prevent dropping parts in the tank. A large rag or towel is best as it will also help catch small parts and prevent them from falling on the floor (where they can be lost).
Remove the two brass screws located on the bottom of the gas cap that hold the latch mechanism in place.
Remove the latch mechanism. Note: there are loose components in the base that covers the latch spring.
Inspect the latch, clean as necessary and then set aside.
There are five small loosely mounted springs on the underside of the gas cap. They can be left in place for this operation or removed and set aside for safe keeping.
Remove the small metal collar located on the end of the key cylinder’s male connector. The collar acts like a bearing between the key cylinder and previously removed latch assembly. It is loose and easily lost. Slip it off and put it aside for safe keeping.
Hold the gas cap vent assembly in place while removing the two short screws located on the base of the gas cap vent.
Wiggle the gas cap vent assembly back and forth to loosen it from and prevent damage to the gasket which is glued to the gas cap cover.
Inspect the gas vent gasket for tears or bulges. The outline of the venting path depressed into the gasket should be visible (this is normal). Gently wipe with a clean cloth. Inspect the cloth used for signs of debris.
Remove the small round plastic check valve/liquid separator located on the underside of the gas cap vent assembly (a pair of small needle nose pliers works well). Be careful not to damage the silicone valve covering the base of the check valve. This is the valve that allows air to enter the gas tank to relieve negative pressure. Remove the check valve gasket as well and place it aside.
Inspect and clean the check valve. Pay close attention to cleaning the tiny 90 degree elbow which leads to the vent hole.
Inspect the silicone valve located on the underside of the valve. It should be soft, pliable and moving freely.
Inspect the small holes behind the silicone valve. Clean as necessary.
Inspect the silicone check valve mounted in the gas cap vent assembly. This valve helps relieve positive gas tank pressure. It should be soft, pliable and moving freely.
Inspect and clean the gas cap vent assembly air channels and vent hole. Pay special attention to the very small vent hole leading to the 90 degree elbow in the small round plastic check valve/liquid separator removed previously. This tiny hole is easily blocked by debris.
Reassemble in reverse order.
Step II: Preventative maintenance.
Repeat Step I frequently (at least once a year) to keep the gas tank vent line free of debris. Keeping the gas tank vent line clean will help prevent debris from reaching the gas cap vent assembly where it can easily block the air channels or small vent hole.
 

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Discussion Starter · #5 ·
redfish,

Hidalgo too has been afflicted by this malady. The most recent time was during my and Daniel's IBA Memorial 1000. It happened in heavy 75 mph traffic on I-20 and was a fairly large 'pucker moment' because we were in the left lane with no shoulder and several short bridges. I managed to get us pulled off of the road without disrupting traffic or getting run over. It took a couple of minutes of cranking to get her fired up again and she ran flawlessly for the rest of the ride.

I am sure that the problem is fuel related by the way she acts. This has happened very intermittently during her life and I believe that is related to the tank vent.

Bill
Bikerbill, I had no idea that Hidalgo was occasionally affected this way too. As to your recent experience, it's always on my mind that the issue will raise its ugly head in a situation similar to yours.

I'm pretty much in agreement that it's somehow a venting problem. From what I've gathered, both positive and negative tank pressure is vented through the gas cap vent valve mechanism. I can gently suck air through it simulating positive tank pressure relief and sure enough hear the whistling sound which I often hear after shutting the engine down. I can also blow through the valve easily simulating negative pressure relief. So the cap mechanism seems OK. Or so it seems. In any event, negative tank pressure relief seems to be the problem and either isn't happening fast enough or not at all sometimes. (But I've never heard any negative pressure "swoosh" sound opening the cap??)

On the tank top, I can also blow air through the two vent inlet tubes - one connects to the cap vent valve mechanism when it is closed and the other beside and outside of the fill opening which is basically exposed to the outside elements. I suppose that one is for any overflow spillage during refueling - that's about all I can tell that vent is for. Now when I say air can be blown through them, it can, but not very fast. I assume that's because of the rubber vent tubes being so long, I guess.

Buy some clear fuel line and install so you can see what is going on.
Sfair, that is a great idea. In fact I would rather have a permanent, clear fuel line between the petcock and the carburetors. I assume there's something available that's heat resistant since it routes so close to the valve cover.

It will be interesting to see if the fuel line is empty when it bogs due to lack of fuel. If I see that, it's either a vent problem or another petcock that fails to operate properly once in a while. ?????

We call it POOGS, phantom out of gas syndrome. Here is a fix for the Vulcan 750.

Subject: Phantom Out Of Gas Syndrome (POOGS)

Symptoms: Motorcycle stalls repeatedly as the fuel level in the gas tank falls below 1/2 full. Symptoms similar to running out of gas. Switching to Reserve has no effect.

Root Cause: Failed gas tank venting system; clogged gas cap vent and/or gas tank vent tube or a failed check valves within the gas cap vent assembly. This prevents air from entering the gas tank to displace fuel being used by the carburetors, resulting in negative gas tank pressure (or vacuum). Negative gas tank pressure prevents fuel from reaching the carburetors causing the motorcycle to stall.
Birdhunter02, I was figuring your 1/2 tank of gas and negative pressure scenario was pretty much on the mark until yesterday when the fuel starvation occurred at less than 50 miles into a full tank; about 3/4 full. That did take me by surprise as it usually occurs, like you say, at about the half tank mark. But I'm sure there are a lot of factors in play here; temperature & barometric pressure & others.

As I mentioned, both rubber vent tubes are not kinked when in place or otherwise obstructed, and are clear as air is passing through them. I'm thinking of shortening both of them and running them to one much larger vent hose. That should make them breathe a little easier.

And thank you for the very nice write-up on the remedy to the Vulcan750 vent system.
 

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Check places like JP cycles. They may have what you want.

The clear line will pinpoint the issue (hopefully) and may/may not save you a cap teardown.
 

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It sounds like POOGS to me too.
You should heed birdhunters suggestions.
It happened to me on my 750 as well. The silicone/Teflon style seals get stiff after years of use and don't work as they should. You need to replace/repair/remove so that you can have a functioning vent system again
 

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Discussion Starter · #8 ·
Hidalgo too has been afflicted by this malady.
Bill
Bill, I'm curious about when Hidalgo happens to starve for fuel. Do you remember if it has ever happened when your auxiliary tank was feeding the carbs? I'm sure you have adequate venting on your extra tank so the gravity feed should always flow. I haven't installed the clear fuel line yet and still kicking around the idea that the vacuum operated petcock may just fail sometimes, intermittently.
 

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redfish,

When the happens with Hidalgo she acts much like she does when she is running out of gas. Except that it begins with a heavy surging instead of an outright power fall off. And it happens well before the point of Reserve. It has happened with a nearly full tank as well as lower levels. But it happens so infrequently that I can't be sure. Regarding the Aux tank, I do have more frequent surging when using it but I attribute it to the fuel flow through the fuel filter and not the vent. (The vent on the Aux tank is a 1/4" line with no valves. It is an open hose all the way.) I have noticed that it seems to happen more often in hot weather. Maybe the fuel molecules are larger and don't fit through the filter as easily. :)

Today I decided to inspect the tank cap and vent system. The line from the cap fitting to the bottom of the hose is clear with no debris coming out at all. The cap itself had no debris in the vent system. This cap uses a red neoprene umbrella style valve. It seems to be clear and pliable. There is also another small hole connected to the vent system that does not appear to be valved. The hole is about 1/16" diameter and is clear.

There was a lot of gunk in the non-sealed areas that I spent a lot of time cleaning, especially the key lock area.

Anyway, the cap is as clean as it was the last time I cleaned it up. We'll see how things go.
 

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Discussion Starter · #10 ·
When the happens with Hidalgo she acts much like she does when she is running out of gas. Except that it begins with a heavy surging instead of an outright power fall off. And it happens well before the point of Reserve. It has happened with a nearly full tank as well as lower levels. But it happens so infrequently that I can't be sure.how things go.
The bad part is you get no warning and never know when it's going to happen.

The eastern US has a fair amount of longer tunnels under rivers & waterways. The thought of losing power in a usually narrow and congested tunnel with no pull-over area in a protected cage isn't so bad, but on a motorcycle, no thanks. This no fuel issue has to be solved one way or the other - it will have to be as close to 100% reliable in that respect as possible.

I have not been into the cap vent mechanism yet. I recall a post by I think Phreon where he goes into detail - will look into that. I'd hate to have to buy another cap.
 

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I have 30,000 miles on my '09 and only had this once, about 3 years ago. Only thing I could see was that the area around the gas cap was a bit wet from previous fill up. So I am wondering if a bit of gas dripped out of the nozzle and entered the vent system, causing the problem. I have been very careful about filling the tank and have not had the problem since.
 

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Discussion Starter · #12 ·
Dpetrick, I can see where that could cause a problem. Googling this issue I found several 500 owners on other forums who claimed to experience the same thing. Trouble is, I can find absolutely nothing wrong with any part of my tank's vent system. Even so, I took the cap vent apart for inspection - it was clean as a whistle. Ha, :eek: I'm going a little buggy with this so I'm going fishing for a week while the new clear tubing ships.
 

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Discussion Starter · #13 · (Edited)
Test with clear fuel line

Buy some clear fuel line and install so you can see what is going on.
Replaced fuel line with 5/16" clear line from Moose Racing - supposed to be high temp tolerant.

Note: These tests were made when the bike was running normally as it never starved for fuel at any time. I couldn't wait until that happened so I proceeded with the tests below.

When installing the clear line I made sure both carb bowls were full and the line was completely filled with fuel - no bubbles. Rode about 8 miles (OAT around 85 deg) at various speeds, petcock in the ON position, and checked line. NO fuel was in the upper half of the line. I don't know how far down into the line it was due to the black plastic sleeve over the line on the bottom portion (it was installed on the original so I put it back on the clear line as well).

There was NO vacuum apparent in the tank when I removed the cap.

Repeated the above making sure the fuel line was full, petcock ON, but left the gas cap loose. Same result after about 8 miles. No gas could be seen in the upper half of the fuel line.

Repeated the above with a full fuel line, gas cap tight, only this time using the Prime position. After 8 miles the gas level in the line was only down about 2", indicating a little air in the line but not much.

Repeated the above tests again on the ON position and the Prime position. Same results as above.

Conclusion: I figure the vacuum operated petcock is not opening fully, but is allowing just enough gas into the fuel line for the engine to run fine, but depending on OAT, barometric pressure, and amount of gas in the tank, sometimes it isn't quite enough. Rare that it happens, but it does.

From this point forward I'll always ride the bike with the petcock in the Prime position. I know pretty much the mpg fuel burn, so the odometer will substitute for the reserve and I'll just have to remember to switch to ON when parking the bike.


This shows how the fuel line looked after several miles with the petcock in the ON position. No fuel can be seen in the upper half of the line.

Thank you all for your input, especially sfair for your line suggestion.
 

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I have a DataPoint for our discussion here. When Hidalgo lost power on the Interstate I had a GPS track being recorded. I checked the track to see where the power loss happened in relation to the last fuel stop.

The power loss happened at 51.8 miles from the previous fuel stop. Approximately 1.5 gallons used to that point based on fuel economy for that trip.

The track also shows about one minute of stopped time so that's how long it took to get her fired up again.

Here's where it happened: N32.69733 W96.26163

'Biker' Bill
 

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Question for everyone who has fought this issue in the past...

Is this resulting in the bike completely shutting off, or just losing power?

I'm having my own issue that is probably unrelated but I figured I would try here first since this thread is pretty active and all about fuel issues!

First ride home on the bike, full tank of fuel, nothing odd happened. Bike rode PERFECTLY. After a bit of goofing around I had gone about 41 miles. Then we got a bit of rain. I ran out to get some things for the wife, figuring this was a good time to get used to the bike on slicker conditions and I ran into my first issue. I'm getting a very random power loss, just for a few seconds, especially at low throttle input. The bike just falls on its face for a moment then picks right back up. It doesn't seem like an ignition issue, because there isn't any backfire from a loss of spark and a buildup of fuel. The engine just goes quiet for a moment, then back to fine again. Annoying and a bit butthole puckering if it happens on the interstate.

I'm thinking it could be a few things.
Water in the fuel.
Trash in the tank clogging the petcock.
Trash in the line clogging the inlet before it splits to the carbs.

It doesn't feel like I'm losing just one side, so I'm not sure its just trash in one of the carbs but I could be wrong.

What say you, Oh great Vulcan Gurus!
 

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Any bucking, sputtering, surging before/after the event?
No bucking before, but yea now that's exactly what its doing. Used some seafoam yesterday, seemed to help after a while of harder riding but this morning it was right back to sputtering.
 

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Check sidestand switch for being loose, out of adjustment, poor connection, etc.

You can test on a temporary basis by shorting two wires together.
 

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Check sidestand switch for being loose, out of adjustment, poor connection, etc.

You can test on a temporary basis by shorting two wires together.
Wow never considered that. Interesting. I'll give it a look see tonight or tomorrow depending on how many cocktails I have. :D
 

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Discussion Starter · #20 ·
Caught it in time!

I've been operating my 500 in the normal petcock "On" position lately when road conditions allow. Yesterday the engine experienced fuel starvation at speed, only 50 miles into a full tank. I quickly pulled the clear fuel line out for inspection while underway while switching to "Prime" (no easy feat!:bad:). The clear line was empty but quickly filled up in the prime position. No pull over was necessary as the engine caught and ran normally.

Back to running in prime position. If only I can train myself to always switch the valve back to "on" when the engine is off. So easy but so hard to remember. :eek:!
 
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