Petcock Failure

Jeffrey Markham automan25 at
Tue Nov 6 20:08:39 PST 2007

On my ride home from work today I noticed the smell of gas. The bike also wasn't running quite right just off idle, a little hesitation. I thought it was the car in front of me with a leak, but it quickly became apparent that it was me. I stopped in a nearby parking lot to try and find the source, but I couldn't. I continued on home and when I parked the bike in the garage I shined a flashlight in to the carbs and noticed fuel leaking from the bottom of the intake shroud on Carb #2. I proceeded to remove the carbs to get a closer look (it is sure a lot easier now that the CA emissions are removed). I noticed some residual fuel around both the inlet and outlet horns on carb #2. This is the carb who's vacuum line is connected to the petcock. So I was assuming that the petcock had failed and that gas was getting sucked in through the vacuum line. After searching the historical posts from this forum though it sounds like when a petcock fails that gas doesn't come through the
 vacuum line, but through the gas line instead. I must admit though, that I'm a little confused as to how gas continuing to flow through the fuel line would be a problem. Wouldn't the valves in the carb bowl prevent any problems with hydrolock? My wife's old CB400F has a manual petcock and when I ride it I often forget to shut the valve off and it's never presented a problem. Someone else also mentioned a leaky petcock causing gas to get into the oil; I don't understand how this would happen it because the gas would seep past the piston rings? Okay, I'm rambling now...any insight as to my problem would be great.


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