eightbit

I don't really know where to start looking here...the victim is a 1975 280Z. I started the car this evening, cranked right over and sounded strong, then died within 30 seconds. I started it again and it would crank over, then die, or hold for a few seconds, do a funny idle wandering thing then settle and then choke. Managed to drive it around the neighborhood, but it would still choke and die. Don't really know if it's something electrical or fuel related. If it's relevant, I just recently purchased the car, with a known issue with the ignition...when I turn the key to the off position, the car won't die and needs a diode wired into the line off the alternator. Just thought maybe the battery was dead, but electrical system seems to be working fine, and the car cranks right over. Also, the previous owner was kinda nonspecific when he mentioned that the emission controls had been removed... so there's stuff physically cut from the engine harness? Also it has a straight pipe with no cat, if that matters. Not experienced with Z cars, I'm not sure if any of this sounds familiar. Since I bought it, the car has run strong...this is a recent dilemma, so I can't imagine what was cut was too terribly important, but than again, I DON'T KNOW. Somebody help a newbie out! I sold a 2002 Civic to buy this Z, haha!