First have you tried moving the throttle since you disconnect it? If it now travels fully it may be simply that the linkage needs moving to the top hole.
As far not starting but have spark have you tried directly placing fuel in the cylinder and see it will hit? If it will not then it can be either a valve not closing or the compression is simply too low. These L-Heads (side valves) tend to close up the valve clearances to a point where the valves no longer close fully.
You need to download a copy of the Briggs single cylinder L-Head service manually for more instructions on troubleshooting and repairs at hand.
