912 Carburetion/Ignition Problems

My Rotax 912 has begun to stumble intermittently at low and high power
settings. I believe that I isolated the stumbling problem to the left
ignition system and removed the double ignition coils, wires and
boots. I checked everything for proper resistances according to the
Rotax manual. Everything checked out fine. I did install a fresh set
of spark plugs at this time. I should add that I was getting erratic
indications on my tach. I did find that my tach lead from its trigger
coil had a bad crimp connector which I replaced and solved that
problem.

Upon reinstallation of the left ignition system, I began to experience
starting problems. My normal start up procedure utilizes the choke to
enrichen the mixture (I have no primer), with the throttle completely
closed. After a couple of blades, the engine will normally catch and
I'll slowly add throttle and simultaneously close the choke for a
smooth and reliable engine start. Now, whenever I attempt to add
throttle or close the choke or both, the engine immediately dies.

I checked the integrity of the "slider" diaphrams on the Bings to make
sure there was not an artificial leaning condition. The rubber
"couplers" to the intake manifold appear to be in good shape, so I
would not anticipate any vacuum leaks there.

Any suggestions would be greatly appreciated.

Tom