Small Engines (Lawn Mowers, etc.): Engine backfires and hunts, fuel tank cap, vacuum leak

Question
Ben,

I have a Briggs n Stratton 15.5 hp ohv engine.  designated IC Platinum on a Craftsman mower. Model 28N707 0173-01.  It stalls while running with the blades on, backfires, and 'hunts' for the proper throttle setting.  After reading a similar guestion from March of this year, I found that the carb is walbro.  Also, I have adjusted the magneto, between .007 and .030, with little difference.( They started at about .025)  I found that the spring that connects the throttle pivot to the choke pivot was stretched.  It measured about 1  3/16", but compressed to about 1".  I clipped a coil off, n got it to just over 1" long. This didn't make a big difference either. Any help would be appreciated.

Answer
Paul

If the Engine operates erratically, surges, and runs unevenly.
Possible causes:

  1. Fuel line or fuel tank cap vent is clogged.
  2. There is water in the fuel.
  3. Fuel pump is defective.
  4. Governor is not set properly, sticking, or binding.
  5. Carburetor needs adjustment or service.
  6. Loose carburetor/intake pipe resulting in vacuum leak.