Compression check, Do's and don'ts Options

[EJP914]

Borrowed a compression tester to see my mechanics results are correct or is he just trying to sell me an engine rebuild. Range went from 100 psi on #1 to 150psi on #4. # 2 and 3 were at 120. Never done this before, but I have removed all spark plugs and the coil wire from the coil to the distrib. Do I need to disable the fuel pump? What's the easiest thing to do, pull a relay or a fuse? Anything else I need to watch out for or do? Thanks in advance for the advice and help!

[Cupomeat]

Ok, so the basics on comp testing is the following;
1. Pull the plugs (all of them to let the engine turn more freely) and pull the ignition power from the coil (or ground the coil wire by removing it from the center of the dist. and touching it to the engine case)
2. Attach the tester to one cylinder and spin the motor with the starter about 4 times.
3. Write the number down, release the pressure in the tester and do it again for the rest of the cylinders.
4. If one or more cylinders is low, squirt some oil in the cylinder to help with diagnostics. If the pressure increases it can often be attributed to bad/worn rings.

I can't imagine that you would care if the fuel pump runs or not, either FI or carbs, as they both won't be sucking much air in, due to the plugs being pulled.

Unfortunately, the rule of thumb is 10% difference between cylinders should result in some action taken to repair the engine, and you have about a 50% increase between 100 and 150, or 33% between 150 and 100, either way, more than 10%.

Good luck.