starting difficulty

For the past couple of months, I have been having a problem starting my 912uls (in a Rans S7s) that is getting progressively worse.  At first it was just slow to catch, now it will not start at all on the left ignition system (it has a soft start module, so normally starts on the left system).  It will start on the right system.  I recently put in new plugs (gapped to 0.66mm) and new spark plug boots, but that did not help.  The battery is new, and the voltage at the starter solenoid when cranking with the ignition off is 10.3, which seems about right.  When I do get it started, if I immediately shut it down before the engine warms up, then start it again, it catches on the first blade.  Once the engine is running it runs fine:  smooth, full power, and about 100rpm drop on each ignition system alone.  I would be grateful for suggestions on what I can do further to trouble shoot.