I've used marvel mystery oil in the cylinders for a few days' then fired an engine up. It will smoke for a bit after but this has always worked for me. About a cup full through the plug hole with a small diameter funnel. Good Luck
You guys out there are the experts. I want to try to >crank up my '67 Rebel SST 343 this weekend. The previous owner says the >car has not been started in over 3 years. Some people say to remove the plugs >and squirt some oil in the cylinders before cranking. Would like your >suggestions. Obviously, I will run my gas line from a clean gas container to bypass >the junk that is in the gas tank. What about the carburetor? Should I >do anything to prep it before firing it up? I also suspect the fuel pump may >not work and will test that. Appreciate any guidance you can give me. >Thanks.