Small Engines (Lawn Mowers, etc.): small engine, briggs stratton, cam lobes

Question
QUESTION: 13.5 ohv Briggs & Stratton 21b807 0239 e1 I have adjusted the valves but the exhaust valve doesn't seem to be opening enough the engine backfires through the intake but for some reason runs at full throttle but it spits and sputters at an idle then dies but starts when you turn the key then dies again

ANSWER: Is the flywheel key sheared?  What are the valve clearance settings?  Is a push rod bent?  Easy way to check a bent push rod it to remove, one at a time, and roll them on a piece of glass...the glass is pretty flat and usually detects if there is a bend in the push rod.

Eric

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QUESTION: Push rods are straight valve clearance is.002 inches the engine won't run when the clearance is .005" the intake valve opens just as far as you can open it without it bottoming out but the exhaust valve only moves about 1/8 of an inch

Answer
Valve clearance should be .004-.006 for both valves per Briggs specs.

The clearance differece will cause timing (mechanical) issues. How old is the engine?  Is the cam wore that much?  Difficult to check the cam lobes as Briggs does not publish specs on the cam grind.

Eric