i kinda have the same problem with my 4ac. mine wouldn't idle so i have to constanly keep the revs up manual, quick gets my foot tiring. well, my 4ac kept on dieing so i took it to the mechanic, he did this and that, fixed it for a few days and same old problem. i started to change different parts this and that and found that my leads were corroded... changed it and it works sweet, wasted all the money at the mechanic for nothing...
i suggest u change your leads, spark plugs, and maybe ignition coil if u got the sapre money.
hope that helps, thats my 2 cents