When I shut off my bike it sucks in air? Any ideas on why?

 

Burnt exhaust valve
Bad head gasket
timing


Changed cams lately by chance?

 

are you burning low octane fuel?

 

You running with straight pipes perhaps? If so, you may have a burned up or seized exhaust valve that isn't plugging up and letting air in.
Does it do this even if you blip the throttle before shutting the ignition?

 

Throw us a bone here...what bike, any mods, recent problems, etc...

 

If you're referring to that brief "fweet" noise when you shut the bike off, it's harmless. Mine does it quite a bit, depending on what stroke the bike is in when I turn it off. I believe it is air being sucked into the air cleaner as one of the pistons drops. I could be wrong about this; maybe someone who knows a bit more will chime in.

 

x2, mine has done it since it rolled off the show room floor even with the stock pipes... just very quietly, aftermarket pipes just help amplify it. I think it's actually the exhaust valve of a cylinder letting unburnt air/fuel mix out through the pipe and it doesnt ignite obviously because the ignition is cut.