Small Engines (Lawn Mowers, etc.): B&S engine, exhaust valve seat, hose clamps

Question
Have a model 402702, type 1205.01 16 hp twin. When cold it starts right up and runs good, if I shut it off it will not start. The starter turns it over real fast, just won't start until cool, (an hour or so).

I took a plug out and they look ok but the spark appeared almost non-existent or weak.

Also when I shut the mower off I get off and as I start to walk away there is always one loud back fire. Not sure if the problems are related. Thanks for the help  

Answer
Hello Leo:

The Backfire is Due to the Gas that gets Sucked Into the Cylinder Just After the Plug Stops Firing is Igniting Inside the Cylinder or Exhaust Port/Muffler. The Carburetor Solenoid is Supposed to Prevent this Problem. The Carburetor Solenoid is Most Likely Stuck in the Open Position and Allowing the Engine to Backfire. Before the Carburetor Solenoids were Installed on these Engines, Allowing the Unit to Idle for 1 to 2 Minutes (Depends on the Heat of the Day and How Hard you have Worked the Unit) Before Shutting Off the Engine Usually Eliminated this Problem. This Can Also be Caused by a Bad Valve Clearance and that would Also Explain the Hard to Start when Hot. Either an Exhaust Valve Seat is Burnt, Loose in the Block or the Valve Clearance Requires Adjusting. Usually I Suggest Setting All the Valve Clearances. If One Cylinder is Causing a Problem; How Long before the Other Cylinder Starts having a Problem. The Statement; "the Starter Turns it Over Really Fast", Usually Indicates a Compression Loss when the Engine is at Operating Temperature. Are the Plugs Firing when the Engine is Hot and Will Not Start? If No, then the Coil/Armature/Magneto is Bad and Requires Replacing. If the Coil/Armature/Magneto is Bad, then Use the Briggs Part #394891 as a Replacement. What are the Cylinders Compression? Does the Engine have the Spring Style Hose Clamps on the Fuel and Vacuum Lines? If Yes, then Change these Clamps to the Screw Style Clamps. The Spring Style Clamps Lose their Tension and will Allow a Leak in the Vacuum Hose for the Fuel Pump. This Causes the Pump to Stop Operating Properly and this will Usually Happen when the Engine is at Operating Temperature. The Following is a General Instruction File for Setting the Valve Clearance, Removing and Seating the Valves on Non OHV Engines. Any Input is Appreciated. **Remove the Carburetor and the Crankcase Breather/Vent (# 8-1) and the Valve (Stem) Cover (# 8-2) so you have Access to the Valve Stems, Springs and Keepers. Set 1 Cylinder to TDC on the Compression Stroke. Using a Blade Style Feeler Gauge, Check the Clearances. The Intake should be .004in - .006in and Exhaust .007in - .009in. If the Feeler Gauge will Not Slide Between the Valve Tip and the Tappet, then you Must Reset the Clearances. **You Will Require a Small Engine Valve Spring Compressor to Remove the Springs and Keepers from the Valve Stems.** Some Engines Use a Valve Keeper that is like Automotive Keepers (2 Cone Shaped Keepers that Set in the Valve Retainer/Rotocoil Assembly)and the Other Style is a Slotted Retainer that is Moved (once the Valve Spring is Compressed) to the Larger Opening in the Retainer and the Retainer Slips Over the Valve Stem Tip for the Valve to be Removed. Remove the Heads. Set 1 Cylinder so the Piston is at TDC on the Compression Stroke And Check the Clearances Between the Valve Stem Tip and the Tappet. The Clearances are as Follows: Intake Valve Clearance is .004in - .006in and the Exhaust is .007in - .009in. You have to Lightly Grind the Valve Stem Tip and Place the Valve Back Into the Engine (you can Hold the Valve Seated by Hand) and Check the Clearance Until you Reach the Required Clearances. Once the Valve Clearances are Reached, Re-Install the Valves on that Cylinder and Turn the Other Cylinder to TDC on the Compression Stroke and Set that Cylinders Valve Clearances.  Once that Cylinder is Set, then Re-Assemble the Engine.** 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