Join Date: Feb 2013
Location: Ossining, NY
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If it's got spark, and the key isn't sheared, my bet is the compression is still low. Briggs flatties with no compression release usually hit at least 90-100 psi. If it had enough compression, it would pop on ether or carb spray. Could be the rings/aluminum bore are worn, the valves needed to be resurfaced before being lapped in, or I guess it could be the head gasket if you didn't throw a new one on there. If you wanna keep chasing this, you might have to look into a ring job or getting new faces cut on the valves/replacing them.
One last thing, did you squirt the ether directly in the spark plug hole? That way you know it's in the combustion chamber 100%. Don't even have to tighten the plug more than hand tight; just get it in there and rip the cord a couple times. If it doesn't even try to start, you're almost certainly not building enough compression.