http://www.onallcylinders.com/wp-con...-reading-1.png
invaluable tool. Between a compression tester, leakdown tester, and a vacuum gauge you can tell everything there is to know about any engine and anytime a suspected engine issue, backfiring, overheating, or low power these 3 basic tests should be run. Easily do all 3 in less than an hour.
Link is a great chart you can print off and pin to the garage wall or wrap the vacuum gauge in it.
Model A has an easy access vacuum port right on the manifold so it cant get any easier.