Small Engines (Lawn Mowers, etc.): B&S 28R707 no joy, sectional index, 6 digits

Question
Ok this is my other mower. Got the previous one running. I have a Murray 30in rider I bought for the grandma-in-law. The engine is a 28R707 1120E1 code 030818ZE. Ran for 2 seasons and now will not start at all. It was run into high ground and stalled. Backfires only
- flywheel key ok
- Have spark
- compression seems ok (finger test)
- getting air
- carb rebuilt (had fuel in oil)
- valves not bent or stuck/ seem to be seating ok
- pcv not clogged
- muffler not clogged
- no binding or loose blade
- seat safety switch ok (have spark)
I can build a V-8 all day but these little engines give me fits. Help! and thanks

Answer
Hello Curt:

>>LOL. A Lot of People have the Same Problem. They can Completely Rebuild a Large Engine, but the Smaller Ones give them a Fit.
>>No Worries.
>>You can View a Breakdown/IPL of this Engine at this Site Addy, http://www.smallenginepartswarehouse.com/parts.asp and Select the Shop Online Parts Look Up. Then Select the Model Tab. Then Select the OEM and Enter the Model (5 or 6 Digits) and Type Numbers (first 4 digits Only). Example: 28R707-1120-E1. Then Double Click on the Model in the Results Area. Select Sectional Index. Now you can Select the Section of the Engine you Wish to View.
>>Here is a Basic Instruction File I am in the Process of Making. It will Might Say Mower, but a Snow Thrower/Blower is Powered by the Same Type of Engine, so the Diagnostics are Basically the Same. >>***Here are some Diagnostic Instructions to Do on the Engine to Locate the Cause/Cure for a Hard/Not Starting Engine. This Does Not Include a Problem with the Valves. If I Suspected the Valves are Involved, then a Separate File for the Valves will be in this E-mail. This is a File in the Making, so Any Input is Appreciated.
>>1- Check the Spark. If Not Firing, then Replace the Plug.
>>2- If the Plug is Firing, then First, Pour a Small Amount of Gas (1oz) Into the Carburetor Throat with the Throttle at Full. With the Throttle Still at Full, Try to Start the Engine. If the Engine Starts and Quits, then Make Sure the Gas is Free Flowing to the Carburetor. If the Gas is Free Flowing, then Remove, Disassemble and Soak the Carburetor Overnight in Carburetor Cleaner (I Use Gunk). I have Found that Most People can Use a Breakdown/IPL and Disassemble the Carburetor Enough for Proper Cleaning. You Only have to Remove the Bowl, Float Pin, Float and Needle Valve and Any Adjustment Screws that Go Into the Carburetor Body. The Welch Plugs Do Not have to be Removed. Then Soak the Carburetor Body and Parts in a 1 Gallon Can of Gunk Carburetor Cleaner Overnight. The Can has a Parts Tray Inside it for the Small Parts. Once the Carburetor and Parts are in the Cleaner, you can Replace the Lid for Safety and to Prevent Accidental Spillage. Then Blow Out the Passages with Compressed Air. Install New Parts if Required.
>>3- If No Fire at the Plug, then Remove the Coil Shut Off Wire from the Kill Switch at the Engine Stop/Brake Bracket (where the End of the Stop/Brake Cable Attaches at the Engine). Check for Fire. If No Fire, then Remove the Blower Housing and Remove the Ground Wire from the Coil. Check for Fire. If Still No Fire, then the Coil is Bad. *On Some JD Model Mower the Engines Use an Igniter. Remove the Igniter and Coil and have your Local JD Dealer Test them for you.
>>* **On Models with Point Set, the Condenser is Bad and the Point Set and Condenser should be Replaced as a Unit. Make Sure the Point Set Plunger is Fully Extended when Setting the Point Set Gap to .020in.
>>** If there was No Response from the Engine When the Gas was Poured Into the Carburetor Throat and the Plug was Firing, then Check the Compression.  If the Compression is Good, the Carburetor has Been Soaked and Cleaned and the Plug is Firing, then Check the Flywheel Key. If the Key is Damaged, then the Plug Firing is Incorrect to the Position of the Piston During the Compression (Power Stroke).
>>*** On the OHV and Some L-Head (Flat Head) Engines there is a Compression Release. The Exhaust Valve Clearance has to be Opened to .020in for the Compression Release Not to Operate; in Order to get a Correct Compression Reading.***
>>From your Description it Sounds like a Bad Flywheel Key. Did you Remove the Flywheel and Look at the Key or Just Remove the Flywheel Nut/Starter Cup and Look at the Flywheel Key. Removal of the Flywheel is Required to Check the Flywheel Key.
>>Please, Do Not Hesitate, If you Hit a Snag, if I Missed Something or this Does Not Correct the Problem, I am Here if You Require More Assistance. Hope this Helps. Let me Know What Happens, Please. May the All Mighty Bless You and Yours. Thanks.

Good Luck

Respectfully

John

>>PS: I am Allowed to Answer 10 Questions a Day. If you See I am Maxxed Out, then Try Submitting your Question at or Just After 8pm EST (US). My New Day Starts then. Comments and Ratings are Greatly Appreciated. Thanks.

Respectfully

John