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Discussion Starter · #1 ·
I bought a 2003 vstar 650 custom last spring. It was my first bike and I rode it every day. It ran fine up until the beginning of winter. The onset of the problem started slowly. I would be cruising at highway speeds (65-70) and suddenly, it lost half the power. Sounded as if only one cylinder was firing. It would slow to 50 mph or so and would maintain it. After I came to a stop, the engine would resume normal operation. This only occurred every now and then. Lately, its getting worse. Every time I ride, as soon as I hit 55 or better for a short time, the front cylinder dies. I know it is the front because when I stop to remedy the issue, I can feel the temperature differences between the exhaust gases between the two pipes. It idles fine, starts right up, and cruises around town with no problems. Only has issues at highway speeds.
The bike has 27000 miles on it. Purely stock except for the cobra drag pipes. I changed the plugs and the fuel filter to no avail. Any help would be greatly appreciated.
 

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It sounds like fuel starvation. Check all the fuel lines for pinching, and the carburetor vents for blockages.

It could be something simple, like the tank vent is blocked, causing a partial vacuum in the tank. Can you have the cap in place, but not fully sealed? If so, give riding it like that a try, but not in traffic; maybe tape the cap in place, so it won't get away. In any case, check around the cap for the vent holes (assuming a non-California model) and make sure they are clear. On an Cali model, there should be a vapor canister connected to the tank through a small hose; if that hose is pinched the tank won't vent.

Next up is fuel pump; if you have one, is the filter before or after it? It could be slowly failing, reducing flow just when you need it.
 

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Discussion Starter · #3 ·
The fuel filter is brand new. It is positioned immediately after the tank. I haven't noticed a fuel pump. As far as vents for the tank, the cap doesn't seal. It just clips into place and is removed by a key. How would I determine if it is a CA model? I live in Texas. It does have an emissions device called the AIS. It insects secondary air into the exhaust port to burn unburned exhaust gases.
I will check the fuel lines as suggested for pinches and blockages. Thanks.
 

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Discussion Starter · #5 ·
It's the stock round paper element. It is also brand new. The design of the housing seems restrictive, but I was told it was necessary to provide the proper vacuum to open the diaphragm in the carbs.
 

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Discussion Starter · #6 ·
UPDATE:
Just went for a ride. It ran just fine. Different story from yesterday. I'm at a complete loss.
 

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Could be you had some water in the bottom of the carbs that got sucked through. I'd run Seafoam through it, as it will remove any water from the system.
 
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