Note: This specifically applies to the '92 - '01 CR250 engine, but it should be adaptable to any 2-stroke. The basic idea is to pull the carb and exhaust, plug one and pressurize the engine through the other to look for leaks.
It's very important to pressure test a 2-stroke after it's assembled. The reason is that a 2-stroke gets it's lube through the pre-mix. An air leak means your engine can run lean. Lean means too little fuel. Too little fuel means too little lube. Too little lube me