Small Engines (Lawn Mowers, etc.): briggs 16 hp twin, hp engine, cylinder model

Question
Hello, a while back you helped a guy with a Simplicity 6216 with a briggs 16hp twin. I have the same one with the same problems, I have done everything I can think of, but still it stalls under load. Any suggestions. I'm sending a copy of his question to hopefully shed some light on the subject...........Question
I recently purchased a used Simplicity 6216 Riding Mower with a B&S 16 HP Engine - Smooth Quiet Twin Cylinder - Model # 402707 0145 01 85081612. When I bought the mower, it would only start by pouring fuel in the carb (priming) and would stay running after it was started, only when the choke was fully on, but would die when the blades were engaged.

In an effort to solve the problem and give the mower a small "tune up", I've done the following:
Replaced Spark Plugs (gapped correctly)
Replaced Air Filter and Prefilter
Replaced Fuel Filter  
Changed Oil
Cleaned/rebuilt carb
After all of this ... the mower still has the same problem, but not as severe. It no longer requires fuel to be poured in the carb (priming) and will restart after it dies, unlike before. I've tried my best to set the mixture and idle speed, but it seems that no matter what setting(s) are used, it still requires the choke for the engine to run with any power. I can get it up to about 3/4 throttle without the choke, but adjusting the throttle too rapidly or giving it full throttle will make the engine sputter and die. Without the choke, engaging the blades at 3/4 throttle makes the engine immediately die.

By opening the choke 3/4 to 1/2 way, I can get the throttle up to full speed without it dying and it seems to be pretty responsive, not as touchy as without the choke. I can also gently engage the PTO to get the blades on and mow a few passes in my yard, but I am still relying on the choke and the keyword here is gently. Any rash changes in speed/throttle can and probably will cause the mower to die.

I've tried just about everything I can think of, removed the carb twice and cleaned with carb cleaner/compressed air. The float seems to be fine, there's fuel in the bowl and all the passageways seem to be clear. Both plugs are getting spark,  All of my symptoms seem to suggest that it's not getting enough fuel, but I am at a loss as to where to go from here.

Do you have any advice that you can offer? Thanks in advance for your time and help.
Answer
Hello Jeremy:

Did you Check the Fuel Shutoff Soleniod? Did you Soak the Carburator Overnight in Cleaning Solution(carburator cleaner)? It takes an Overnight Soak to Properly Clean a Carburator. Spray Cleaners just Loosen the Varnish inside the Carburator. Reclean the Carburator. You can View a Breakdown of the Engine at this Addy http://www.outdoordistributors.com/ and click on the B. Then Select Briggs and Stratton. Then Select Dont have Part Numbers. Then Scroll Down to the #40 and Click on it. Then Scroll Down to the 402700 File and Click. This will Download a Breakdown of the Engine. Hope this Helps. I am here if you Require more Assistance. Let me know what Happens, Please. I enjoy knowing the Outcome. Thanks.

Good Luck

Respectfully

John  

Answer
Hello John:

Wow; You Did Go Back a Ways in My Answers. I was Still Spelling Carburetor Wrong. lol. One thing I Forgot in My Answer to Jeremy was to Check the Compression. If the Compression is Bad (on Either Cylinder), then Check the Valve Clearance (the Clearance is between the Valve Stem Top and the Rocker Arm). 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). 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 the Valve Clearance is Good, then Check for a Bad Head Gasket. You can Use the Same Site Addy I Gave Jeremy to View a Breakdown/IPl of this Engine. Please Remember that Soaking the Carburetor is the Only Way to Ensure the Carburetor is Clear of Varnish and Trash in the Jets and Internal Passages of the Carburetor. Hope this Helps. I am Here if You Require More Assistance. Let me Know What Happens, Please. Thanks.

Good Luck

Respectfully

John