i have a '72 240z.

when i crank the engine, it takes a while to start, and then when it starts it will only go up to around 300 or 400 rpm, and if you touch the gas, it stalls.

if you wait, sometimes it'll stall, sometimes it'll get up to speed,

but once it's hovering around 1000 rpm, if you touch the gas it'll stall.

i do not have an air filter, would that have anything to do with it,

and also, would an air filter from a '76 280z fit on my '72?

A 76 is fuel injected and a 72 has carbs so no to that question. I would attempt an answer the first question if you car was fuel injected but since it's a 72 I'll have to defer to the carb guys.

Think simple first..... How is your fuel delivery to the carbs? Is your fuel filter present, clean, and showing 1/2 or better full when you are cranking/running? Are the carbs clean.... have you had the domes off to clean them out and de-carbon the pistons? (Don't mix them up. Do one at a time.) I assume you are using the choke, but it's worth asking to be sure. If so, check to make sure the choke cables are actually doing what they are supposed to do. The FSM and most other manuals have procedures to check that out. If you can eliminate these simple things up front and still have a problem, this forum will be a great place to help you through it.

Let's make sure you've got 'fuel', then move on to the 'spark' part.