Had mechanic do compression test on my '73 1.7 w/ stock FI. Results were #1 100psi, #2 120 psi, #3 120 psi, #4 150psi. Says I need valve job. Car seems to run Ok except for one hell of a backfire on decelleration and acceleration around 3500 RPM is a bit ragged. How do I know if this guy did this right? Are there any conditions (engine too hot or too cold when tested) that would cause these kind of numbers? Before I give my car to this guy, thinking about a second opinion. I think someone is just after my money. Maybe not???? Appreciate the opinions.

Buy a tester and do it yourself. We'll help.

If he or some other garage has a leak-down tester, pay to have it done. It will isolate the problem if there is one.

Compression should be done on a warm engine. Throttle wide open and crank. Values should be within 10% of each other.

A compression test won't tell you that you need a valve job. It will only tell you that the compression is lower in one or more cylinders. It could be leaking past the rings, the valves, or the junction between the heads and cylinders. A leakdown test will tell you much more accurately where the leakage is because you can hear the pressurized air escaping- either through the intake, the exhaust, into the crankcase, or out of the heads.