RE: Welcome to Club SAITO !
Ah, castor oil. For that "Get Up and Go" feeling.
Treehanger, that build up is considerable and the worst I've seen in a long time. You must have been putting out enough smoke to hide the Normandy landings! All that does lead towards the suspicion either a sticking valve or some of that getting between the valve face and seat. Drop it in a crock pot of glycol and it would come clean in a few hours.
As for starting, I find mine sans choke need a slightly open throttle to start, (still below 1/4). Once fired off and warmed for a few seconds it can be brought back down.