My friend has a 1970 Oldsmobile cutlass He’s change the spark plugs but it still cuts out when you give it gas. Do you think it could be the timing is off . If the timings off would it cause it to cut off like that. we’re not sure if the timing is right. Have you had experience using the timing checker from AutoZone
It could be a lot of things, for example a weak or nonfunctional accelerator pump in the carb or a vacuum leak. Unlike modern cars everything runs "open loop", all settings need to be done manually and there is nothing to compensate for anything being a bit off.
Timing certainly needs to be set correctly for the engine to run properly and it's easy enough to check, there should be plenty of youtube videos showing how to do it. If your friend intends to keep the car a timing light would be a good investment, as would be a factory shop manual.
If it has not been converted to electronic ignition a dwell meter would be nice as well, but not really necessary with the hex-key adjusted points used in GM 8-cylinder distributors. There is an old-school method of doing it by ear: Turn the hex key clockwise until the engine just starts to stumble, then back out 1/2 a turn. You set the timing after you set the dwell since the dwell angle affects timing.
Is the engine running rough or knocking/ pinging? Did your friend happen to save the plugs? They can give you a really good idea on issues with the motor. Especially your mixture quality. My '79 Catalina was running super rich, the plugs looked powder coated, I'd blow faint black smoke out of the tailpipe, and I was getting 8 MPG.
If the engine is running relatively smooth at idle, it sounds like a fuel/ air mixture problem. Check the functionality of the accelerator pump in the carburetor. It's easy to do, with the engine off, pull off the air cleaner cover, manually open the choke plate and look down in the throat of the carburetor while your friend pushes on the gas, or manipulate the throttle yourself. If the pump is working correctly, you should see a pretty good stream of gasoline spray inside the throat of the carb. If you don't, That could be your issue.
For vacuum leaks, your friend should inspect and replace all of the vacuum hoses if they're old. Spray carb cleaner around hoses and vacuum ports with the engine running and listen for the idle to change. If it does, you found a leak. Opening the throttle with a bad accelerator pump or having vacuum leaks can stall the engine, since they can let more air than fuel in, to the point where it's no longer combustible.
As @chucktobias suggested, get a service manual for the Cutlass, I paid $25 for a digital copy of GM's dealer service manuals for my Catalina on RockAuto. It's been a spectacular source of info.
I would put my money on a new mechanical fuel pump, filter and a carburetor rebuild kit (with a float level adjustment and a new accelerator pump diaphragm.) Also make sure the choke linkage is cleaned and adjusted and functioning properly (electric, vacuum, etc.)
