I have a very nice 1963 Corvair 900. It runs great. Starts great when cold,and runs good, but when warmed up driven 15 or so miles and shut off it starts very hard. Cranks good, but just won’t fire. till cranking too long to be good for the starter. Will finally start.any suggestions?
I am thinking you may have fuel boiling in the carburators or vapor lock after a hot soak. You will have to determine if the problem is because of a rich or lean condition. When the problem occurs look down the carb throats and see if you can see fuel burbling out of the main nozzle. If you don’t see fuel coming out operate the throttle and see if the accelerator nozzle squirts. If you suspect the carbs are not getting fuel, squirt some starting fluid into the carbs to see if you get a catch. Also make sure that the choke plates are open and are not closing too soon.
Also if you still have the point’s ignition make sure that the points, capacitor, cap, rotor, wires and plugs are in good condition as the ignition can be weak on starting. However, usually ignition problems crop up on cold damp starts.
It has been a long time since I have worked on one of these – or for that matter driven a Corvair.
This is way out there, but…
Was the gas tank out? I knew a car once that had a gas tank vent line that was pinched and it did the same thing. That car had such a strong fuel pump that it actually partially collapsed the tank. I wonder if you would hear a rush of air when loosening the gas cap after running it a while?
Sometimes you have a condition where you just get the wrong setting from the automatic choke. New thermostatic spring(s) could solve the problem or repairing the metal vacuum lines that used to go to a source of heat. I think the choke is closed too far at hot start.