1953-1960 Classic Car Engines Troubleshooting Guide: Engine Misfires At Low or Idle Speeds
Things to Look For:
Faulty spark plugs.
Spark plugs gaps too narrow.
Dirty or corroded secondary circuit connections or faulty ignition cables.
Cracked or faulty distributor cap. Radial contacts in cap burned or worn.
Dirty air cleaner.
Ignition point gap too narrow.
Faulty carburetion due to: (a) float level too high or too low; (b) float valve leaking; (c) incorrect or loose jets; (d) restricted or partially clogged idle air passage or jet; (e) air leak occurring between upper and lower carburetor body; (f) air leak occurring around carburetor throttle shaft.
Air leaks in intake manifold or carburetor resulting from: (a) loose manifold connections or leaks occurring in vacuum lines; (b) loose manifold nuts or capscrews; (c) broken or damaged intake manifold or carburetor gaskets; (d) cracked manifold; (e) warped or damaged manifold contacting surface.
Slight leaks occurring at fuel pump check valves.
Air leak occurring around intake valve stem because of excessive valve stem-to-guide clearance.