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Join Date: Apr 2008
Location: Wayne, NJ
Since the petcock is a vacuum feed type, you need to provide suction on the vacuum line in order for fuel to flow. When I drained my tank, it was off the bike, so I had more options. With it on the bike, I've heard of 2 different methods, and I'm hoping that someone who has actually tried this jumps in! The first was to siphon the gas out of the tank. The second was to set the petcock to RES, disconnect the 2 fuel lines, and attach 2 hoses to the petcock nipples and route them into a fuel container, and then use a manual pump on the vacuum line to provide suction and get the fuel to flow into the container. I would also drain the carbs and use about a half can of seafoam in the next fill up to clean out any residual stuff from the system as well.
I am thinking that you can also be experiencing a problem somewhere in the ignition/fuel system. Have you checked the plugs to see if they are fouled? In general, the way I understand backfiring, there is a problem in the spark/air/fuel balance. Bad/no/poorly timed spark could be to blame. Clogged air filters, or a blockage in the air intake, could cause you to run too rich. Finally, a problem with the fuel delivery, like a stuck float, could be the issue. Since the bike is running poorly, I am assuming that excessive air getting into the exhaust is not causing the backfire.
I would try a new fill up to eliminate bad gas as the culprit. Then work through the ignition and fuel system until you find the trouble.
I am pretty new to this stuff, so I hope some of the more experienced folks chime in here! Good Luck!
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