Small Engines (Lawn Mowers, etc.): Valve adjustment, briggs stratton, lawn mower repair

Question
Hello Sir,

Thank you for taking the time to read my question.

I have a Yardman tractor with the 15.5HP Briggs & Stratton I/C Model 28N700 engine.  I believe it's a 1996 or 1997 model but has only been used for 6 summers and has never given me problems and I keep it well serviced.  Air filter is fresh as well as the oil.

Now I have 2 problems.

1.  It all of a sudden began running poorly, lost idle, ran loudly backfiring through the carb.

I shut it down and pulled the spark plug and it looked fine. I pulled off the air cleaner and started the engine and it really backfired loudly through the carb and would barely idle.

I called the local lawn mower repair shop and they said it sounded like a 'rod' had come loose and they have a 4 week backlog.

Well being a fairly adept back yard mechanic, I decided to investigate.  I pulled the head and the piston works fine, the valve look fine, just a bit carbon coated.

So question number one is - can you tell by the symptoms what is causing this engine to all of a sudden run poorly?

Now comes problem number two.

2.  I pulled off the rocker cover and found that one of the caps on the spring was out of place, so I slipped it back on decided to put it back together, see if that was the problem, and if not, take it to the shop.  Well, I couldn't get the pushrods to line up so I unbolted the rockers, counting the precise number of revolutions that I backed them out, but I did that wrong.  I backed them out using the set screw unbeknownst to me that is waht it was - a set screw.  Needless to say, now my valves are out of adjustment and I don't even want to take it to the shop torn down like I have it.

So question number two is - How does on adjust the valves?

I would appreciate your advice.

With best regards,

Brad

Answer
 Hello Brad:

 1- The Carburator was Likely the Cause for the Backfiring and Running Poorly. Improper Fuel to the Engine (lean mixture) will cause the engine to Backfire and Run Rough and Not Idle Properly. 2- Set Piston to Top Dead Center. the Valves are Set at: Intake .013in and Exhaust .017in. This is a Little Wider than the Book calls for but, I have found with these Settings I dont have to Reset the Gap after the Valves and Components have Seated in. Hope this Helps. Let me know what Happens, Please.

 Good Luck

 Respectfully

 John