A common complaint is "won't start", "one cylinder seems cold", and variations of the same. Basic troubleshooting is to determine whether the fuel system or ignition system is at fault before chasing dead horses.
The first thing to look at is the sparkplug(s). If the tip(s) is wet it indicates fuel is being delivered to the cylinder(s), although it might be excessive.
Next, lay a new plug(s) on the head(s) making sure the metal portion of the plug base is grounded. Kick it over, with ignition on, and see if there is a visible spark. Note: spark can be weak and not fire under compression.
If there is no spark, ignition is at fault and needs attention.
Note: 100-200vac should be present on each HT coil (+) with kickover on CDI ignitions
If spark is present, and it is a single cylinder problem, then swap carbs from one cylinder to another to confirm a carburetor problem.
If cylinder fires with a spray of starter fluid at the intake it is an indication that it is a fuel problem rather than ignition.
A timing light can be attached to each plug wire to see if spark is present or intermittent. (Actual setting of timing is not required... just watch light flashes.)
In addition, clogged exhaust (especially Wirges chambers) can cause problems, more apparent at higher rpms.
Common Ignition Problems:
- Kill switch on
- Bad or fouled plugs
- Weak battery (S series & early H1)
- Contaminated point contacts (S series & early H1)
- Bad/corroded connection at plug cap
- Resistor type plug caps/ wires/ plugs
- Improper gap of plugs and/or magnetic pickups
- Defective ignition module (CDI)
- Defective lo/hi speed coil windings (CDI)
- Defective Ignition coil
- Missing ground to motor wire on rubber mounted engines
- Crossed ignition wiring
Common Fuel Problems:
- Poor cleaning of carburetors/jets
- Improper float setting
- Leaking float valve
- Leaking floats
- Lack of carb sync
- Improper air screw setting
- Clogged petcock filters
- Clogged fuel cap vent
- Slides installed backward
- Improper choke plunger setting
- Brass "BB" plug missing at intake
Holed pistons/excessive "pinging" is a result of lean fuel mixture and/or timing advance.
Seizures are normally a result of a lack of oil to the cylinder.