Small Engines (Lawn Mowers, etc.): Engine has loss of power; backfires, loose hose, valve clearances

Question
I have a Poulan riding mower, B&S 18.5 HP, engine model # 1P777, serial # 040930ZE, Type C299C1. The engine was running fine until it backfired through the carburetor. The blades were not engaged. Since, the engine has had a significant loss of power and continues to backfire. Where do I start?   thanks

Answer
Michael

Sounds like a fuel pump problem but first check that all the line fittings from the tank are tightly clamped. A loose hose will allow air into the system. Also check the impulse hose between the crankcase and pump for deterioration.You may want to check the carb to see if is too lean. Three things you might try - new spark plug, gasoline aditive such as SeaFoam (to clean carb passages and carbon) but first, remove or loosen gas cap on gas tank, See if that makes any difference.

Also you may want to check the valve clearance? I set my valves at .05 and .07 intake and exhaust. on my 17hp briggs intek engine because i think it breaths better with a little more clearance at the valves. Hot carbon deposits in the cyl. can cause backfiring at certain times of the cycling of the engine. Just another way of looking at these things.If the fuel tank is above the engine, a fuel pump is not needed. The clear fuel filters cause a lot of problems,
as many who watch the fuel travel, or seemingly lack of
travel, through them, automatically assume the problem is
fuel related.
In your case, I would advise ignoring the fuel filter,
but instead, cheack the valve clearances, as that is
quite possibly the problem.