This is a standard problem on high rev'ing 2 strokes.
Air has mass. And since it has mass it also has momentum.
When the inlet port opens you get a high speed rush of air going into the engine. When the inlet closes that rush of air hits the closed port and bounces back through the carb. If you have run without an air filter you can see the spray around the carb inlet. It looks like a stationary cloud of fuel-air mix but it is actually cycling in and out at the same frequency of the engine rpm.
There is not a lot you can do. A longer inlet track might help but sometimes it is not practical. Try a larger air filter.