What does your plug tell you? It should be chocolate colour, but WOT(wide open throttle) can be different than puttering around. Triple check for air leaks first, spray some wd-40 or brake cleaner around your intake, if idle changes you have a leak.
Now this could just be a case of a bad vent in your gas-cap, it can happen. Pull your cap when your symptoms start to see if it goes away... If it is a bad vent, drill a little hole to remedy that... if not, read on.
It could also just be from vibrations causing the fuel in the bowl to 'foam'... there are many threads around on vibrations. Check the google search at the top for more info on that.
I forget what this test is called, but what you want to do is bring your plug removal tool with you on a cruise. You get up to top speed at WOT and kill the engine at full speed. Don't let it kick-over at all. Stop and see what colour you plug is. *Do not pull a plug from a hot engine*!! Aluminum threads will come off with your plug when hot!! Head to a pub or a nice spot to take a couple pictures
You see, when you're above 75-80% throttle you're metering needle is all the way out, and you're running on 'straight jetting' so run your test and see what your plug tells you, and get back to us.
