If you guys think its unburned fuel in the exhaust, & that's why it smells so strong when running, pull your plugs & see what color they are, that'll tell you if you're running very rich. Check your vent hose on your gas tank also. I'm guessing a fuel leak would be pretty easy to spot, & you'd smell fuel long after the bike was off. But only smelling fuel when its running, I'd vent looking at vent lines or a possible very rich running condition as the cause of the smell. One last thing, make sure your gas cap is properly sealing, it could be venting fumes there also, but more than likely it would leak there as well.