Total Motorcycle Community Forums

Hey all,
Just got a new(er) bike last week, and have only ridden about 1000km on it, but I've discovered a slight issue with it. The first time I took it out on the highway, it was running great until 220 or so km on this tank of gas. It started surging a little bit (not drastic, just a slight loss of power, then a couple seconds later it came back on again). I thought maybe I was out of gas, but the fuel light hadn't come on yet. I switched to the reserve anyway, but it didn't seem help. It went away for a bit, then came back, etc. Anway, I stopped for gas at the nearest station, filled up, and went on my merry way without probelms. Just over 200km later, I had the same thing start happening. By that time I had gotten to calgary and arrived home so it left my mind for a bit. My dad took out my bike for a quick spin, but didn't mention any surging problem.

On the weekend I rode around a fair bit, but I filled up twice more, both close to the 200km mark and both times without drama. Then this morning, on my way back to medicine hat, I had the same surging start up again, also around the 200km mark. I pulled in to the nearest gas station, shut the bike down, and went to fill it up. However, after trying to get the pumps working for a few minutes, I discovered there wasn't anybody inside the store and the pumps were completely shut off, even the pay-at-the-pump ones. So I started the bike back up and continued riding, and lo and behold, no surging. So I guess the first couple times it happened, it wasn't the filling up with gas that solved it so much as stopping and shutting off the bike.

I'm thinking I might replace the fuel filter if the bike has one (04 honda 599) and see if that helps, but is there anything else I should check? It feels like someone just let off the throttle a bit when it happens, so I'm guessing it's running lean sometimes, hence the fuel filter suspicion...

Surging whilst cruising does indicate a slightly lean condition.
Check and double check all your hoses from/to the tank and carbs. A vaccuum leak can also cause these sort of problems.

This sounds like it could be the dreaded clogged fuel tank vent. Every time you open the gas cap, you let air into the tank, which masks the vent problem. Next time it starts surging, pull over and open the gas cap. Then close it and see if the surging is still there.

Thanks, that sounds like it would cause exactly those symptoms. Maybe i'll bring my spare key with me next time i go for a highway ride and try opening the tank when it starts doing that so I can eliminate the fact that shutting the bike off does it.

Hope you plan on doing that while stopped on the shoulder
*Pictures rider trying to open fuel tank at 60mph*

Yup, my buddy had a similar issue on a Kawa ZX9. Ended up that a vacuum hose from the tank was disconnected. 5 minute fix

Ok, so I finally got a chance to confirm that opening the tank for a second did in fact make the surging go away, so it is most likely the tank vent that is clogged (and for your amusement mgdavis, yes I did it while riding 70mph , but it's pretty and safe to do when you have a 50km straight section of highway going through the prairie with perfect visibility and no traffic around).

Anyway, how do I unclog it? I think compressed air would be easiest, but I don't have an air tank or compressor (should really pick one up). I also don't really know where the vent is on the honda 599, though I assume its the little tube that runs down inside the tank from a little hole next to the filler neck. Any tips?

Tank vents differ from bike to bike. Some vent at the filler neck and some vent through the cap. It sounds like you've found the one on your 599 (though I'd verify that with the shop manual). If your vent system is built into the tank, compressed air sounds like the way to go. I highly recommend draining the tank first and keep in mind that as you blow air into the tank, highly volatile fuel vapors will be blowing out. Some folks will even fill the tank with water after draining, to purge fuel vapors. Stay far away from any potential ignition source.

Although unclogging a vent sounds simple, this might be a task that is better suited for your local shop. They are better equipped for the task.