Small Engines (Lawn Mowers, etc.): 17.5 Briggs & Stratton, valve lapping compound, briggs stratton

Question
17.5 B&S Model 31c707  0026G1 Code:090402ZA The engine is 2 yrs old. I've been doing this for awhile this one has me stumped. Had to replace flywheel key do to bad gas and back fire. Motor has 10 hrs.on it. Valves are set carb is clean as precaution and fuel solenoid works. It burns and exhaust gets warm but won't fire up. plug is new and plenty of spark. coil gap is proper. Could a valve be fried? Also proper torque on flywheel is set. what should the compression be on this engine. I don't want to have to tear the engine apart just yet. Could the flywheel key have messed up already? I've gone over everything but sometimes it's like it's flooding itself out but there's nothing to these carbs and it's clean as I said. Have any ideas I need some help here. THANKS Jim

Answer
I would check the flywheel key again.  It's rare to shear keys on the larger engines.  If you need to you can use some valve lapping compound and lap the flywheel/crank to make sure the parts are matched.  I've had to do this in the past.

Have you check the valve clearance?

You can download the service manual from the site below?

http://bgsengineclinic.com/brochures/276781SingleCylinderOHV.pdf

As for compression, Briggs rarely publishes compression specs.  They use cylinder leakdown test for testing engine compression.

Is the engine under warranty?

Let me know if the flywheel key is sheared and what the valve clearance is.

Eric