Small Engines (Lawn Mowers, etc.): snowthrower carb replacement, adjustment screws, snow throwers

Question
My neighbor's snowthrower required a new carb due to a cracked mounting flange. The engine is a 5 hp Tecumseh snow king. The original carb was p/n 640084A. The shop gave him a p/n 640084B.(replaces the"A" p/n carb) This replacement carb has no adjustment screws at all. The engine runs fine until you try to throw snow. Then the rpm's drop, it backfires, sputters, and quits. The governor seems to be working ok. When you engage the auger, the rpm's increase. When you start to throw snow, the governor pushes the lever on the carb to it's stop, but it still seems like the engine is starved for fuel. Any sugestions?

Answer
It does sound as though it is starved for fuel and I'm a little concerned the new carb has no adjustment.  Because snow throwers work in a cold (and broad) temperature range, they need to have adjustment to enrichen the mixture the colder it gets outside.  He is going to have to get the correct carb because his only option is replacing a fixed jet or drilling out the existing one but both of these fixes are a bad idea because it will run poorly at a warmer temperature.  Hope this helps.