Boy, does my son's slant run crappy!

If you believe it to be running lean, check the fuel pressure and the filter. If you believe it is running too rich check the float. Moisture can affect old wires caps and rotors so check them, and be sure the distributor isn't loose and timing has gone out of adjustment. Other probs I have had in the past with poor drivability are EGR valves, leaking vacuum lines, bent distributor shafts, and timing chain issues. If it has been running bad for weeks it is it is going to be a basic issue with any luck. It may just need a tune up.