Troubleshooting the VL
This how-to article applies to 1930-1936 Harley Davidson V series motorcycles and originally appeared in the rider's manual
SUMMARY OF MOTOR TROUBLES AND THEIR CAUSES
The following information will serve as a guide when trying to locate the trouble in a motor that doesn't start or run right.
Missing at High Speed
Missing at high speed is usually due to poor carburetion—carburetor not properly adjusted or some of the vital parts loose or worn out. It may also be due to any one of the following causes:
- Defective spark plugs—porcelain cracked, point gaps adjusted wrong, or fouled and in need of cleaning. Try new plugs.
- Gasoline pipe clogged, or the cock partly closed.
- Air vent (small hole) in gasoline filler cap plugged.
- Sticking valves, due to carbon in valve guides.
- Broken or weak valve springs.
- Valve tappets improperly adjusted. Read how to adjust valve tappets
- Circuit breaker points out of adjustment. Read how to adjust points
- Circuit breaker points worn away.
- Insufficient breaker lever spring tension.
- Defective ignition coil.
- Faulty condenser.
- Discharged or broken down battery.
- Loose wiring connections around battery, generator, ignition coil or circuit breaker.
- Chafed or poor insulation on wiring, causing a short circuit.
Missing at Low Speed
May be due to any one of the causes described under "Missing at High Speed," but more likely due to one of the following:
- Loose manifold connections.
- Carburetor throttle shaft badly worn. Causing air leaks.
- Carburetor loose on manifold.
- Leaky cylinder head joints.
- Spark plugs fouled, or their gaps improperly adjusted.
- Carburetor adjusted too lean or too rich. Read how to adjust carb
- Too much oil in crank case.
- Poor compression, due to condition of piston rings and valves.
If the Motor Refuses To Start
Failure to start is likely due to one of the following causes:
- No gas in tank, or gas not getting to carburetor.
- Carburetor loose on manifold.
- Carburetor adjusted too lean.
- Fouled spark plugs; clean and adjust.
- Defective spark plugs; try new plugs.
- No spark; see if a spark will jump from ends of plug cables.
- Dirty, worn out, or improperly adjusted circuit breaker points.
- Storage battery discharged; see if lamps will light.
- Storage battery disconnected; look for loose wiring connections or broken wires; crank motor with ignition switch ON and see if ammeter indicates discharge, as it should, when circuit breaker makes contact.
- Switch box not grounded.
- Damaged insulation on wiring causing a short circuit. (Ammeter would indicate heavy discharge.)
- Defective ignition coil.
- Faulty condenser.
- Valves or ignition timed wrong.
- Clutch slips and prevents motor from being turned.
- If it is impossible to turn the motor over with the starter, the trouble may be that the motor has been run without enough oil, until the pistons or piston rings have become seized in the cylinders.
- See if you can locate any of the faults mentioned under "Missing at High (Low) Speed."
If the Motor Shows Loss of Power and Overheats
Overheating and loss of power are likely due to one of the following causes:
- Spark lever does not advance all the way.
- Improper carburetor adjustment; probably adjusted too lean.
- Excessive carbon deposits in combustion chambers.
- Poor compression due to bad valve seats, cylinders.
- Weak exhaust valve springs.
- Valve tappets not adjusted properly;
- Defective spark plugs.
- Clutch slips or brake drags.
- Gear ratio too high for the locality or kind of service. package truck, be sure the machine is geared properly.
- A poor grade of lubricating oil is being used.
- Either too much or not enough oil in crank case; drain
- Bad air leak around carburetor, manifold or cylinder head joints.
- Muffler clogged; keep the slots cleaned out.
- Valves or ignition improperly timed.
Back Firing or Popping in the Carburetor can be caused by:
- Motor not sufficiently warm.
- Carburetor choking device set in running position too soon.
- Carburetor adjustment wrong; mixture too lean.
- Inlet valve tappets adjusted too tightly.
- Exhaust valve tappets adjusted too loosely.
- Weak inlet valve springs.
- Faulty ignition or ignition timed wrong.
- Muffler clogged.
- Circuit breaker points too close.
