Before you diagnose: 60-second checklist

• Verify base timing and that your advance curve isn’t excessive
• Check for vacuum leaks (intake gaskets, carb base, hoses)
• Confirm fuel pressure and clean fuel delivery
• Verify cooling: fan/shroud/radiator size, air bleeding
• Confirm grounding and ignition component health

Most issues become obvious after those checks.

1) Overheating (traffic and idle heat soak)

Common causes: weak fan setup, no shroud, undersized radiator, air trapped, lean mixture, too much timing.

Fix:

• Upgrade fan + shroud first (it’s often the real problem)
• Bleed cooling system properly and confirm thermostat operation
• Verify timing and mixture (lean + aggressive timing = heat)

Prevention: build cooling for worst-case traffic, not highway speed.

2) Oil leaks (valve covers, pan, rear main)

Common causes: old gaskets, poor sealing surfaces, crankcase pressure from PCV issues.

• Use quality gaskets and correct torque pattern
• Make sure PCV is working (pressure pushes oil out)
• Inspect sealing surfaces for warping

3) Lifter tick / valvetrain noise

Common causes: low oil pressure, incorrect preload, dirty passages, worn components.

• Confirm oil pressure with a known-good gauge
• Verify rocker preload/geometry
• Use correct oil viscosity and keep it clean

4) Hard hot starts

Common causes: heat soak, vapor lock, too much timing, weak starter wiring/grounds.

• Improve grounds and starter wiring (voltage drop kills starters)
• Shield starter and route fuel away from heat
• Re-check base timing and advance

5) Off-idle stumble / hesitation (carb)

Common causes: accel pump shot, transition circuit tuning, vacuum leaks.

• Verify accelerator pump and linkage
• Check vacuum leaks (intake/carb base)
• Dial idle mixture and transition circuit

6) Misfire under load

Common causes: weak ignition (cap/rotor/wires), plug gap, fuel delivery, timing curve.

• Inspect plugs, wires, cap/rotor, coil output
• Verify fuel pressure and clean fuel filters
• Verify advance curve isn’t too aggressive

7) Low oil pressure

Common causes: thin oil, worn bearings, pump/pickup issues.

• Use correct viscosity for your build
• Confirm pickup/pump setup and clearances
• If persistent: investigate bearing clearances (deeper diagnosis)

8) Oil consumption / smoke

Common causes: PCV pulling oil, valve seals/guides, ring seal issues.

• Verify PCV system and baffles
• Smoke on decel often points to valve seals/guides
• Ring seal issues require compression/leakdown tests

9) Fuel leaks / odor

Common causes: old hose, poor clamps, routing near heat, carb inlet sealing.

• Replace with fuel-rated hose and proper clamps
• Route away from headers/heat sources
• Inspect carb inlet, fittings, and filters

10) “It runs, but feels weak”

Common causes: timing curve wrong, vacuum leaks, fuel delivery, gearing mismatch.

• Verify timing and advance curve
• Check vacuum leaks and carb baseline tune
• Confirm fuel delivery under load
• Match gearing/converter to RPM range (big cam + tall gears = lazy feel)

Composite customer stories (examples)

These are common scenarios (not verified purchaser quotes).

• “It overheated only in traffic.” Fixed with a shroud + stronger fan setup and correcting timing that was too aggressive.
• “It stumbled off idle.” Found a vacuum leak at the carb base and corrected accelerator pump settings.
• “It felt weak until we fixed gearing.” The cam and RPM range didn’t match tall gears; corrected combo and drivability improved immediately.

350 Problems FAQ

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