[john hall]

It is beginning to sound more of an electrical issue. Wondering if its something odd like a damaged wire making poor/intermittent contact to the coil or to the points. You have done a lot to the fuel system, why not go over the ignition with a fine tooth comb as well. If this is to be a weekly mower it wouldn't be wasted time to replace anything in question as well as having peace of mind as to its condition.