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Discussion Starter #1
I've been reading about the fuel starvation issue but I think this is something else -- maybe some of you can help me out. It's an 06 En500 LTD with about 20K miles.

Took a long weekend trip and noticed toward the middle part that the bike just sounded a little "different" at lower speeds (<50 mph). This might be just because I could hear it at that speed, but it sounded more throaty, almost more Harley-like if that makes sense. But performance wasn't affected so I figured I'd check it out when I got home.

Next I noticed while waiting in line for a ferry that the idle would occasionally do something in between a rattle and a buzz, almost more of a dull ringing sound from the engine, and at the same time the revs would increase on their own a little. This is in neutral or with the clutch all the way in. My mind went to valves?

Finally, once at ~30 mph and then a few more times at highway speed, the bike lost power momentarily and it seemed a lot like the fuel starvation issue some folks are describing. Maybe it's a separate issue, but the first time it happened, at ~30 mph, the bike died completely. Pulled over, restarted fine. Then at hwy speed it just lost power momentarily, then lurched when it "caught." Did this several times in a row, then back to normal. Fuel was at least 1/2 full all instances. One time, I thought I heard a "Pop" from the left pipe but I couldn't be sure.

Could it be the plugs?

Thanks for any thoughts.
 

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Your thought on valves - no.
Plugs for the rest - replace them cant hurt, but dont think so.

The end of your post seems a lot like the POOG problem.
For that the tank lock and the tank vent needs looking at.
The vent tube can become clogged with road crap at the very end.
 

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I'm having more or less the same problem. 05 Vulcan 500, 15k mi. I've discovered it has to be some kind of vent issue but it seems to only affect the L cylinder. I can ride for approximately a mile before the cylinder will cut out - power goes way down (well, in half) and it starts with the loud choppy sound. I can pull over, open the tank and power will come back for about another mile. (L & R cylinders as the rider sits on the bike)

I know which cylinder it is because the L exhaust tube (at the exhaust flange) is cool enough to touch after a long ride, the R is hot.

I took the tank cap apart and there's a small diaphragm in there - everything looked okay, if it's like a chainsaw carburetor diaphragm though "looks alright" can be deceiving, I suppose. Cleaned out the channels, didn't change anything. To the vent tube, is that the 2 small holes in the mouth of the tank where the cap closes? I sprayed some - well it was seafoam, I didn't have anything that I thought was okay for rubber, otherwise. Got a little drippage out of 2 tubes that terminate near the rear tire. I intend to take it into the shop next week and blow it out with some compressed air. Anyway, a plugged vent inside the tank doesn't quite fit since it only affects 1 cylinder, and so rapidly - although the speed could be from the fact the tank is about 80% full right now.

My other notion was that I saw on the R carburetor there is some kind of vacuum hose that comes from the air switch valve that sits on top of the valve cover, under the tank. But the L carburetor has a that hose coming from the fuel tap. What exactly goes on there?

The POOG syndrome described on this forum only kind of fits, since it just affects 1 cylinder. But gas is definitely having trouble getting to the L cylinder, sometimes.

Also like to add that I am a small engine mechanic; I understand all the concepts at work here, I'm just new to how exactly they apply to a motorcycle. Thank you.
 

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Discussion Starter #4
I'm having more or less the same problem. 05 Vulcan 500, 15k mi. I've discovered it has to be some kind of vent issue but it seems to only affect the L cylinder. I can ride for approximately a mile before the cylinder will cut out - power goes way down (well, in half) and it starts with the loud choppy sound. I can pull over, open the tank and power will come back for about another mile. (L & R cylinders as the rider sits on the bike)

I know which cylinder it is because the L exhaust tube (at the exhaust flange) is cool enough to touch after a long ride, the R is hot.

I took the tank cap apart and there's a small diaphragm in there - everything looked okay, if it's like a chainsaw carburetor diaphragm though "looks alright" can be deceiving, I suppose. Cleaned out the channels, didn't change anything. To the vent tube, is that the 2 small holes in the mouth of the tank where the cap closes? I sprayed some - well it was seafoam, I didn't have anything that I thought was okay for rubber, otherwise. Got a little drippage out of 2 tubes that terminate near the rear tire. I intend to take it into the shop next week and blow it out with some compressed air. Anyway, a plugged vent inside the tank doesn't quite fit since it only affects 1 cylinder, and so rapidly - although the speed could be from the fact the tank is about 80% full right now.

My other notion was that I saw on the R carburetor there is some kind of vacuum hose that comes from the air switch valve that sits on top of the valve cover, under the tank. But the L carburetor has a that hose coming from the fuel tap. What exactly goes on there?

The POOG syndrome described on this forum only kind of fits, since it just affects 1 cylinder. But gas is definitely having trouble getting to the L cylinder, sometimes.

Also like to add that I am a small engine mechanic; I understand all the concepts at work here, I'm just new to how exactly they apply to a motorcycle. Thank you.
Yeah, that sounds different from what I have. For me I didn't need to open the tank cap, I just pulled over and restarted and it was fine. Also, I went several hours at highway speeds and didn't notice any big difference -- I doubt I'd be able to do that normally with only 1 cylinder firing. But it may somehow also be related to the same issue. Maybe those instances of losing power were one of the cylinders missing, or the plug not firing, or something...

Headed out of town this week but will look at it more when I get back.
 
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