it's cavitating for fuel. When they get into the air, they lean out a lot. Richen it some more. You might need a tach to help you tune it. Get it to peak, then richen it until it drops 3-400 rpm. Try that. You may also have an airleak somewhere. Will it die with your throttle kill button? Whenever I have an engine that does that in the air, I always richen it a couple of clicks and send it back up. That's usually all it takes. Remember, this time of year, one day you fly it might be 35 degrees, and the next time you fly might be 80 degrees and 90 percent humidity. All of that accounts for the tuning. I own the evo 46. I haven't flown the 100, but have a 100 four stroke that will act the same way if it's too lean. What prop are you turning with it?