choking too much gas

Can anyone help? Mazda B2200, original owner. Vehicle choking, as if it has too much gas, rich. 150,000 km, only 12,000 km on rebuilt engine, have put in: re-built distributor, flushed and put in tested used injectors, oxygen sensor, think it is mass air flow sensor but runs when disconnected, computer not giving read out, but reads out when disconecting known parts. Had recently put on new muffler and tail pipe, catalytic convertor was clogged, replaced with new. Fuel has been checked. Turns over and runs a few seconds then chokes. Any ideas. Hate to bale on it.