need help with my 305 v6

[Blakeman350]

So I started working on my 67 305 v6. I've rebuilt the card, new spark plugs, new fuel filter and cleaned the gas tank and put new fuel in it. Here's the issues, when I try to start it it back fires through the carb and then when it does start it will only run up to between 1500 and 2000 rpms. I also made sure to double check the vacuum line was hooked up on the carb. I didn't check to see if there was any vacuum before I shut it off. Aside from parts being hard to find and expensive I don't know a whole lot about these engines so a point in the right direction would be great.