I too suspect the sometime difficulty with starting is with technique rather than mechanical/electrical/fuel fault.
My own VW with 'armstrong' starter isn't usually a problem when cold or hot, though when warm it can be a little difficult.
Cold, open throttle, full choke, ignition OFF and suck in through 8 to 12 blades, depending on how cold, summer cold or winter cold, then allow to sit for about 30 seconds or so, set throttle and it will normally fire in a blade or two.
Hot, switch on and swing the prop pretty much does it.
Warm, meh, it often likes 2 maybe 4 blades with choke, open throttle, magneto OFF , then a couple of blades with no choke and open throttle, magneto OFF. You can do those last couple of 'clearing' blades backwards if you're nervous. A short pause before going for a start usually is beneficial too.