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Discussion Starter #1 (Edited)
Hello,

Have a 2006 Vulcan 500, 6,000 miles, that has just started to backfire. The backfire has occurred twice now (in the last 3 days). I've done some work on cars (but not so much carburetor). This is mainly my wife's bike, that I drive only a little bit.

With the first backfire, she's not positive where the first backfire came from, but it occurred when she was decelerating for a stop sign, and may have let off of the throttle a bit too quickly. The second backfire came from the rear side of the carburetor (i.e., away from the gas tank), and occurred when accelerating from a stop light, when she may have let off the clutch too quickly without giving enough throttle (i.e., the RPMs may have been a bit low). My wife said twice in the last couple of weeks (out of about 12 starts) the bike started a bit rougher than normal (i.e., would need to turn over the starter longer to get the bike to fire. The weather has begin to cool a bit in Northern Indiana, with temps being in the low to mid-60's when starting the bike in the mornings.

We've owned the bike for about 3 years (and she put around 1,000 miles on it in that timeframe). We do store it over the winter with some fuel in the tank, but have always used fuel stabilizer, and the bike has always fired up OK in the Spring. We've done nothing with the exhaust, and it is the original factory exhaust system that appears clean and in good order (at least from the exterior).

I was thinking of doing/checking a few things before looking in detail into the carburetor, and looking for thoughts as to whether I'm starting down the right track:

1. Put some carb cleaner in the gas tank, in case there are some small amount of varnishing in the carb jets.
2. Replace air filter to make sure engine getting enough air.
3. Replace fuel filter to ensure no clogs (And engine getting enough fuel).
4. Check (and replace?) spark plugs.

In the last year, I've noticed that periodically while running (every 90 sec. or so), and about a minute after the bike is shut off, there is a slight whining sound coming from near the gas cap. i'm not sure if it is pressure release, or sucking air in to stop a vacuum in the gas tank. My guess is that as the fuel is used, the cap is vented to suck air into the gas tank to stop a vacuum. I didn't know if this was normal, or if I may have a gas cap vent that is failing. Is there a way to check the gas cap venting?

And along those lines, if the gas cap venting is starting to fail, could this be causing the backfire (i.e., causes a vacuum in the gas tank that prevents as much fuel from getting into the carb (and then the cylinder) causing a lean condition?


Any thought are appreciated.
 

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1. At that age, it is time for the carbs to come off, cleaned, inspected, any suspect parts replaced and adjusted to Kawasaki specifications.
2. The whistling is normal. When you shut the bike down, engine heat rises and heats up the fuel in the tank and builds pressure. The cap will vent this pressure.
 
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