I'm trying to figure out why my 1985 4BBL T/A w/ 305 is misfiring on me, the other day it was in the garage while I was looking at my water pump (Which had to be replaced, and was) and my car just stopped right then and there, went to start it up, and it was misfiring and making a deep rumble, the rpm gauge was all over the place. Fuel pump, fuel lines are all good, carb is throwing fuel in, spark plugs are all good. Whats my problem? any help would be awesome.

 

The tach bouncing all over the place can be a sign that the pickup coil is going out. Take a look at your distributor, check the cap and rotor and especially see how much play is in the shaft.

A new pickup coil runs around $10 or so but a reman dist is only around $100. For a 25 year old dist it may be best to swap a new one in.

When's the last time you replaced the plug wires, cap and rotor? These are also all wear items that should be routinely replaced like the plugs.

 

Check the plug wires, they may have burned on the exhaust or rubbed off on something. Also look for a vacumn leak you may have knocked off a line somewere. Cap and rotor could need replacing.
You never said if it had a tune up or not so start looking at that.

 

It was the Ignition coil, thanks guys for the help!