Small Engines (Lawn Mowers, etc.): Yard Machines riding lawnmower engine dead?, briggs stratton, hp briggs

Question
I have had a Yard Machines lawn tractor powered by a 20 HP Briggs & Stratton V-Twin, model 407777, type 0184E1, code 020301YG. It began loosing the ability to be started by the key first, so I threw in a manual starter switch (the key still had to be in the 'on' position for it to run). Then the mower began to run roughly- I tried replacing line/hoses, spark plugs,etc, to no avail: however, when I removed the wiring harness from the key switch it ran wonderfully. I used the mower like that for a year or so. One day I was mowing and had to stop, so I throttled to low and choked it (the normal method to stop the engine without the key any longer being attached).  When I went to start, it did not. That was about two years ago. I have been trying to fix it since.  I have removed and disassembled/ cleaned the carburetor (by the overnight soaking method) and replaced plugs again. I found that the fuel shutoff solenoid in the fuel bowl had locked into a closed position, so I removed the solenoid and put a bolt in its' place, ensuring that there was enough clearance to allow the normal functioning of the carb. That got the engine to the point where I could eventually get it to start: it would run exceptionally roughly and at a low speed regardless of the throttle setting. It would not start when choked, only when un=choked, and would not respond to moving the throttle. When I would throttle up by hand on the carburetor it would speed up, then drop down, then speed up cyclically and fail to maintain speed. Today I took off the valve covers and, lo and behold, on the non-fuel pump side the top pushrod had come off the rocker arm and was stuck in the hole. Removing the rocker arm and pulling the rod with pliers allowed me to replace the pushrod. The engine then started on the second try with the throttle at slow, not at all with it in fast or when choked to any degree. The engine would not throttle up at all, however. Various ammounts of messing with the valves has not helped today. It now backfires a lot when I try to start it and if I can get it to run it will smokily idle at low speed and eventually dies and cannot be restarted when it is hot. I have called local repair shops in search of a new carburetor but I am not convinced that this is the problem at all.  What can I do here beside replacing the engine?

Answer
Hello Rik:

What are the Valve Clearances Set to? Did you Set the Valve Clearance with the Engine at TDC? Have you Checked for a Blown Head Gasket between the Cylinder and the Push Tube Galley? You Need to have the Valve Clearances Set Properly before you can Continue with More Diagnostics. I Do Not Use the Setting Called for by the OEMs. I have Found that the Following Works Best. Remove the Valve Cover (on the Dead Cylinder for Twin Cylinder Engines). Set the Cylinder you are Setting the Valves on to Top Dead Center (Both Rocker Arms will have Play in them when the Engine is at TDC) When Setting the Valve Clearance. Now Loosen the Valve Adjuster Locks and Set the Intake Valve Clearance to .004in -.006in and the Exhaust to .008in - .010in. I have had Better Performance Out of the Mowers and Less Burnt Valves Using these Settings. If you Hit a Snag 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. Thanks.

Respectfully

John