I have a B&S 12.5 HP I/C Engine Model 289707 Type 015401. I've never had a problem with the engine until I tilted the mower up to change out the steering wheel and shaft. Steering wheel is successfully installed. The engine had a hard time cranking so I adjusted the carb. I replaced the air filter. At this point, I've adjusted the carb all the way down and then backed off 1 1/2 turns. The engine runs fine without the air filter for about 3 minutes. Then a puff of grey smoke and the engine shuts off. There is oil and gas residue in the carb. Any help would be greatly appreciated? Thanks!!