Before running any test check for the obvious stuff like a loose spark plug wire, pinched or loose vacuum hose, bound linkage, etc. If you are convinced all the superficial components are OK then use this rule of thumb when diagnosing an engine:
- First test for compression. Compression test & leak down. Ensure the valves are properly adjusted.
- Second test timing. Ignition timing, spark plugs, wires, etc. Plus cam timing if you even suspect it is not correct.
- Last check the fuel system (carbs or FI) including linkage, and any areas that can be adjusted, wear, or fail. Be sure to test the fuel pump and if suspect test the fuel pressure/volume.
Diagnose in this order to ensure you eliminate possible problems than could be masked or falsely diagnosed as other systems. I can not count the number of owners I have met who spend weeks or months chasing "carburetor problems" only to discover their valves were not properly adjusted or their timing was off or something else amiss that they and everyone else were 100% positive was a fuel issue when it was not.
If you fix/replace components try to make changes to one system at a time if you can. Then drive the car and note any positive or negative changes before moving on to the next issue. You want to create a baseline and ensure each system is correct before moving to the next. In this way, when and if you do isolate your issue to a Fuel Injection issue you can tackle it with confidence that you will be able to find and fix the real problem.
One last thought, sometimes it may be only one issue effecting an engine and other times it may be a few little things that add up to poor running. If you go through the diagnostic process you can start to rule out certain things and this will make it much easier to find the true fault or faults.