give a squirt of fuel through the carb to start the engine. the engine should run a couple of seconds on the prime. if it does, probably a carb/tuning problem. if it doesn't, inspect the crankcase and backplate for possible cracks or warped backplate allowing an air leak. I don't think it is a fuel line problem or carb problem because the problem followed from from your friends plane to you with a perfectly good carb from your engine. IMOH, there is possibly an air leak or missing gasket, something along those lines.