It's likely that the air vent built into the gas cap isn't working properly or the vent line, one of those rubber hoses that hangs under the bike has become clogged. When this happens, at times of higher fuel consumption rates like on the highway, a vacuum actually forms in the tank stopping fuel flow. Had this on my 800 and fixed it by disassembling the gas cap and removing all the vent components. Kinda radical but I was disgusted with the problem.

 

Had this on my 800 and fixed it by disassembling the gas cap and removing all the vent components.

Thank you for your time in replying.

Were you able to test the cap to be certain that this was the problem? Once the vent was removed did it still form a good dam to gas sloshing out of the tank, or water out?

What you are saying makes sense as a possible cause. I haven't enough experience with bikes to know where to look for issues.

Can the cap be easily replaced? Can it be replaced by aftermarket parts (to avoid waiting for shipping of stock parts)

 

Thank you for your time in replying.

Were you able to test the cap to be certain that this was the problem? Once the vent was removed did it still form a good dam to gas sloshing out of the tank, or water out?

What you are saying makes sense as a possible cause. I haven't enough experience with bikes to know where to look for issues.

Can the cap be easily replaced? Can it be replaced by aftermarket parts (to avoid waiting for shipping of stock parts)

Ya it a vapor lock. I had to mod mine.
There is a small plastic disk.. it's the size of a hole punch from a notebook.
Remove the 2 screws for the gas cap and remove the other screws.. pull the cap off and you will see it there. remove it and reassemble.

I had no problems at all after that...
and no.. gas will not slop out after that mod...

 

Excellent,

Thank you both for your assist. I will let you know how it goes. First I have to get my bike back from the garage. They have been closed over the holiday weekend, hopefully they haven't tinkered with it yet.

 

Sounds like a classic Vapor Lock or a Venting problem.

 

If you overfill the tank, gas will splash into the tank cap venting system and stop it up causing the problem you describe. You should not fill the tank past the filler neck.

 

If you overfill the tank ...

Yep, that checks. The mileage to get to and from work is such that I fill the tank as close to full as I can to make sure I can always fill at the station where gas is the cheapest. I have already removed the little plastic disc as recommended above. I have not yet been on the road to note if it has fixed the problem, although after reading your post I wonder if I ought to have just left it in; or for that matter if I should reassemble it.

What advantage/disadvantage is there to leaving the little plastic disc out of the cap?

 

What advantage/disadvantage is there to leaving the little plastic disc out of the cap?

Advantage is your bike won't quit at highway speeds. Disadvantage is you won't be meeting all those nice people on the side of the road.

 

ON the 500 it is almost always a loose battery terminal that causes this .. I found out the hard way with my wifes bike.. was pointed to the battery by a past thread I found... check the battery terminal 95% sure it wil be loose.. I tighten hers up every 6 months now and the issue never reappears

 

Yeah, if it's not vapor lock, it's the battery. Mine wasn't fully charged and a day or two on the charger fixed it. However, I didn't have to stop and prime, it would just shut down while riding, then kick back on.

 

seems like I had the same problem with my bike the other day on the freeway. It suddenly shook a little bit and decelarated itself for a little while and a short burst of accelaration again. This repeated several times and that kind of scares me a bit. I thought I'm running out of gas. So I stopped by the gas station and fillled in about 4.3 gallons so obviously it was about 1 gallon left in the tank when that happens. so I don't think it's about the gas.
I remember the day before I had my bike down to one side when I made a sudden stop at the corner right turn to avoid a stupid car coming out of nowhere. The bike is intact and able to start right away. It could be the gas fill into the breather tube when it was down. I rode on the freeway after that but don't see the hesitation problem again. But after reading this post, I would look at the breather and also try to remove the vapor disk in the cap.

 

Thank you all for your experience. I believe the problem was vapor lock as many of you have suggested. I have now been through four additional tanks and have not had any resurgence of the problem since I removed the little plastic disc from my fuel cap. What a relief to have an affordable fix to this problem.

Thank you once again.