Continuous misfiring. The most likely source of trouble is the spark plugs, but a second possibility is low compression. Check as follows:
[1] First determine that the current is flowing to each plug; remove the plugs and check-for dirty electrodes. Clean and adjust spark gap, or replace the plugs as necessary (par 17).
[2] Inspect high tension wires. Replace them if wet or if their insulation is swollen or has deteriorated (par 18).
[3] Remove the distributor cap and check for burned electrodes or cracks. Replace cap if defective (par 19).
[4] Conditions contributing to low compression will also cause misfiring in one or more cylinders. If the remedies given above do not correct the trouble, check the compression of all cylinders (par 9) and make whatever repairs are necessary.
The above and the references to paragraphs are from Automotive Trouble Shooting For WW2 Vehicles, Volume 1.
Automotive Trouble Shooting For World War Two Wheeled Vehicles, Volume 1, is a useful manual for anyone. Do you know what to do when the cranking motor will not crank the engine? Engine fails to start? No spark? Misfiring at high speeds or under full load? Problems with your battery or battery cables? Do you know how to adjust your breaker points? Inspect the coil? Do you know how to polarize the generator? Use a jump wire to test your main light switch? Adjust your headlights? Trouble shoot your carburetor or fuel pump? All these and much more are covered. Put a copy in your truck for those little roadside emergencies!