If your float adjustment is incorrect, there is slightly too much gasoline in the carburetor. This is not a problem with a cold engine; however, when the engine is warm, it may run too rich. If you turn off the car now, the gasoline in the carburetor will heat up and expand, thus overflowing into the manifold. If you then restart the car, the spark plugs will get wet and the car will flood.

Vapor Lock. The fuel turns into vapor bubbles, preventing gasoline from being pumped into the carburetor. Older mechanical fuel pumps suffer from this more than modern electric pumps. Sometimes shielding the fuel lines and the carburetor can help. Modern gasoline has a lower boiling point, which makes you more susceptible to vapor lock.

Vapor lock is often caused by the float needle and/or the return valve in the fuel pump not sealing properly. If the pressure in the line drops rapidly, the fuel will boil faster because the boiling point is also raised due to the increased pressure. Vapor lock is difficult to diagnose.

If the valves are too tight, you lose compression. Often (though not always), the engine will continue to run. Sometimes it runs somewhat irregularly, and you lose power. If the engine then stalls, it will not start again due to the low compression. After cooling down, the valves close again, and the car starts normally. Pay extra attention to this with recently reconditioned engines and LPG cars. These need to be checked more frequently!

The ignition coil can short-circuit if it gets hot. The windings then lie tighter against each other, making it harder for the insulation. You can test this by inserting a spark plug directly into the coil cable of a warm engine/coil and holding it against the engine. If you get a spark, the coil is in order (and therefore the ignition is also working).

If you do not get a spark with the same test, you are losing the spark in the distributor cap. Then either the distributor cap is dirty or damaged, or the rotor is broken. Also, look closely for black streaks, cracks, or stains on the distributor cap.