[Kahuna]

As many have said, an AF gauge is an excellent tool. Essentially, a bung is welded into the exhaust head-pipe on one side (or both). An O2 sensor is then screwed into the bung and an AF meter is then hooked up for tuning. When not in use, a plug is screwed into the bung, and no-one is the wiser. Some people leave it installed as a means of constantly monitoring the engines' fuel mixtures.