This same event happens on my 2011 MTS ABS. Sometimes there is an obvious "woosh" of air, and other times not as much ?
Have you done a canisterectomy? If not, you may want to check your canister as it may be plugged up with something, or since it's somewhat erratic, maybe gas is filling it some times and not others. This can happen if you overfill your tank (i.e. putting fuel in past the lower end of the neck of the filler opening).
I still have that damn canister. I guess it is time for surgery !Have you done a canisterectomy? If not, you may want to check your canister as it may be plugged up with something, or since it's somewhat erratic, maybe gas is filling it some times and not others. This can happen if you overfill your tank (i.e. putting fuel in past the lower end of the neck of the filler opening).
In any case, both for your bike and the OP's, a whoosh of air when you open the cap is a sign if a plugged vent hose. On the 1200, the vent hose(s) are connected to the bottom of the cap and route forward under the tank cover. They are easily pinched if you muck with them and aren't diligent about ensuring they aren't pinched anywhere when you put the tank cover back on. DAMHIK.....
-SM
Might want to check the tank vent under the passenger seat. The float valves in them have been known to get stuck.
This is on the 09 mts1100
Not to get TOO far off topic, but I've had nothing but trouble with those damn things. The main issue is how everything is plumbed. Basically, any fuel that sloshes up and would run out of the vent hose instead gets sucked (via vacuum from the throttle bodies and a 1 way check valve) straight into the throttle body, causing surging. Here you have a finely tuned fuel injection system that is metering out fuel based on air temp, TPS position, and exhaust gas composition, then along comes a random amount of fuel at a random time into the mix. Stupid.
This made my Guzzi buck so bad it was nearly unrideable in first gear at low throttle openings. Once I removed the canister, it was like a new bike. Also, they can get plugged up with excess fuel or other crud and cause tank pressure issues, similar to what the OP is experiencing. I realize they are there due to EPA laws and in theory are good for the environment, but until they are better designed and implemented, mine will continue to "fall off" my bike shortly after bringing it home.
