Rough Idle

The term "rough idle" means that the engine does not run smoothly when idling. The most likely cause is an over- rich mixture but any defect which produces uneven explosions or missing will cause a rough idle. The most common causes are:

• Dirty idle jets and passages.
• Rich idle adjustment.
• Dirty air cleaner.
• Float level too high.
• Choke set too rich.
• Fuel volatility too high or too low.
• Substantial air leak into intake manifold.
• Fuel pump pressure too high or too low.
• Clogged carburetor jets.
• Ignition point gap too narrow or much too wide.
• Spark plug gaps too narrow or too wide.
• Sticking breaker arm.
• Weak spark which permits some missing.
• Leaky engine valve.
• Sticking valve or rocker.
• Broken valve spring.
• Insufficient tappet clearance.
• Hydraulic tappet holds valve open.