Finally experienced the gas tank "vapor lock"

Everything in-between the gas cap and the carbs. Also how the engine inhales.
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Triangles
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Finally experienced the gas tank "vapor lock"

Postby Triangles » Fri Jul 02, 2010 9:59 am

If you are not aware, it is common for the vent in the gas cap to occasionally not vent creating a vacuum and causing the bike to stall from lack of fuel even though there's plenty in the tank.

I've had my '06 EN500 for a little over a year and while riding she began to sputter like she was running out of gas. First red flag was that I was only at 99 miles, but I switched to reserve anyway. Still didn't fire so I pulled over. Checked the vacuum line on the gas petcock and it was ok. Next I opened the gas tank and sure enuff I could see plenty of gas. Tried to start her again and she sputtered back to life. Made it a half mile or so down the road and she started sputtering again. I immediately pulled in the clutch, turned off the key and opened the gas cap, put the key back in and let out on the clutch she fired back to life again. I rattled/tapped the gas cap in an attempt to shake the vent valve loose, pulled the key out of the ignition to close the gas cap, put key back in and let the clutch out to refire the engine. When I stopped at the next light I could hear the gas cap singing to me so I knew my problem had been fixed which was a good thing since a quarter mile down the road I was getting onto rush hour expressway traffic.

In hindsight and for hopefully obvious reasons it probably wasn't very smart or safe for me to be fiddling with the gas cap not to mention having an open gas tank while still rolling down the road.
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Re: Finally experienced the gas tank "vapor lock"

Postby GeorgiaRider » Fri Jul 02, 2010 3:01 pm

Thanks for the update. Hasn't happened to me yet.
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Re: Finally experienced the gas tank "vapor lock"

Postby burkbuilds » Fri Jul 02, 2010 8:55 pm

Hey, maybe that's what happened to me Wednesday evening. I left school about 5 o'clock and took old highway 41 to avoid as much Atlanta I-75 traffic as possible for a while but somewhere just before I hit Cartersville, my bike started acting like it was out of gas, at 88 miles since fill up. I pulled over to the side and tried starting her, but she just turned over and wouldn't fire. I already tried going to reserve when it started to die and that hadn't helped. I checked the fuel level visually, no problem, then I pulled the seat and started checking fuses and the battery terminals. Nothing blown or loose. Tried to start her again and she fired off and ran fine the rest of the way home.

kawboyCAFE
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Re: Finally experienced the gas tank "vapor lock"

Postby kawboyCAFE » Sat Jul 03, 2010 12:38 am

just so you guys know, it might not be the gas cap. the most probable cause of this is the vent lines under the seat. i had this happen to me, and i re-routed the vent lines under the seat because they were getting pinched between the seat and frame causing the tank to not vent. now that i have moved them a little, this problem does not happen to me. give it a try, this will probably fix your problem.

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Triangles
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Re: Finally experienced the gas tank "vapor lock"

Postby Triangles » Sat Jul 03, 2010 11:49 am

kawboyCAFE wrote:just so you guys know, it might not be the gas cap. the most probable cause of this is the vent lines under the seat. i had this happen to me, and i re-routed the vent lines under the seat because they were getting pinched between the seat and frame causing the tank to not vent. now that i have moved them a little, this problem does not happen to me. give it a try, this will probably fix your problem.


Good thing to keep in mind if it happens again. I'm pretty sure in my particular case it was the cap since the bike was roasting in the sun all day in the parking lot and then the flow thru the vent would reverse when I rode it home.
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Re: Finally experienced the gas tank "vapor lock"

Postby Dustbuster » Sun Jul 11, 2010 9:11 am

Triangles wrote:
kawboyCAFE wrote:just so you guys know, it might not be the gas cap. the most probable cause of this is the vent lines under the seat. i had this happen to me, and i re-routed the vent lines under the seat because they were getting pinched between the seat and frame causing the tank to not vent. now that i have moved them a little, this problem does not happen to me. give it a try, this will probably fix your problem.


Good thing to keep in mind if it happens again. I'm pretty sure in my particular case it was the cap since the bike was roasting in the sun all day in the parking lot and then the flow thru the vent would reverse when I rode it home.


I've had both happen. First time was the vent line under the seat. I had just done the check on the battery. Most recently on Friday afternoon. Bike sputtered/died about 5 miles out of town. In this case I had a low fuel level, about 20 miles from reserve and it was almost 110 f. at the time. I expected to hear something when I opened the fuel cap, but maybe it's just not that loud (modular helmet)? However, it started right up after, and fine the rest of the trip home. (once I remembered that the bike won't do anything while in gear without the clutch)

I need to look at how to reroute the vent line, I'm pretty careful now when reinstalling the seat but if there's an easier way I'm for it!
Not far from San Diego, Yuma is closer, can't get much farther south...

kawboyCAFE
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Re: Finally experienced the gas tank "vapor lock"

Postby kawboyCAFE » Sun Jul 11, 2010 8:03 pm

i will get a pic of how i did mine on here shortly. it will be a few days before i get my camera back, but i will get them shortly.

shadowguy
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Re: Finally experienced the gas tank "vapor lock"

Postby shadowguy » Tue Jun 26, 2012 6:43 pm

Mine didn't quit on me but probably just because I was only riding around the neighborhood. It was over 100 degrees in Little Rock yesterday and I took my older son out riding on his new Ninja 650 (nice machine-not really new though-an '08 with 14,000 beautiful adult ridden miles :D ) with me in the lead on the Vulcan. I'm supervising him for a few days as he just got his license. We rode for a half hour or so and when I shut the Vulcan down in the carport I could hear a hissing sound coming from the gas cap. I opened it and the pressure equalized and shortly after it started hissing again. I'll try to run down the line under the seat and see how that is situated but I'm not sure what to do if the vent in the cap (I assume there is one?) is blocked so any suggestions there are welcome. Is there anything else I should check? Thanks.
Just because you're paranoid doesn't mean they aren't out to get you.

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Re: Finally experienced the gas tank "vapor lock"

Postby Triangles » Wed Jun 27, 2012 12:26 pm

The hissing sometimes squealing is normal you don't need to do anything. IIRC the valve in the gas cap that causes the hissing some times gets stuck and doesn't allow air back into the tank when the pressure is reversed. Then when you are riding you literally run out of gas because the vent doesn't allow air into the tank as gas is used up and you get a partial vacuum that prevents gravity from pulling gas down to your carbs.

The noise you hear is from the heat causing the gas to vaporize and pressurize your tank and then is slowly vented thru the gas cap.
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shadowguy
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Re: Finally experienced the gas tank "vapor lock"

Postby shadowguy » Thu Jun 28, 2012 12:24 pm

Ahhh, that explains it then. Thanks. I'll quit worrying about it unless something happens to make me need to worry. My younger son will be taking the MSF Basic Rider Course in mid-July and then will be purchasing the Vulcan from me and I do want to make sure he is able to enjoy many miles of issue-free riding.
Just because you're paranoid doesn't mean they aren't out to get you.

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Re: Finally experienced the gas tank "vapor lock"

Postby Triangles » Mon Aug 11, 2014 10:47 am

It's been about 4 years but my bike picked an very in opportune time to start doing this again. There is about a 20 mi. stretch of I-75 where they are widening it to 6 lanes by adding two in the middle. They have two lanes each direction currently with the cement block wall on one side and grass or guardrail on the outside. In other words there's nowhere to pull off. I pleasantly happen to need to go down this to get home with very heavy traffic moving about 60-65mph. I would make it a couple miles and stall out! I would quickly take the key out, pop the gas cap open-close, then back in the ignition. All while rolling down the highway trying not to cause too much of a jam up. I was very happy to be out of this mess. I will have to check to see if the vent tube is getting pinched or if I have to take apart the gas cap.
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