Note: this repair manual includes troubleshooting codes and flow charts, plus color wiring diagrams on CD, as well as most chapters.
Book Excerpt: 2006-2009 Harley-Davidson FLH, FLT Touring Series Repair Manual
SPARK PLUG READING
Reading the spark plugs can provide a significant amount of information regarding engine performance. Reading plugs that have been in use will give an indication of spark plug operation, air/fuel mixture composition and engine conditions (such as oil consumption or pistons).
Before checking the spark plugs, operate the motorcycle under a medium load for approximately 6 miles (10 km). Avoid prolonged idling before shutting off the engine. Remove the spark plugs as described in this chapter.
Examine each plug and compare it to those in Figure 67 while referring to the following sections to determine the operating conditions.
On carbureted models, if the plugs are being read to determine if carburetor jetting is correct, start with new plugs and operate the motorcycle at the load that corresponds to the jetting information desired.
For example, if the main jet is in question, operate the motorcycle at full throttle and shut the engine off and coast to a stop.
TABLE of CONTENTS:
General Information
Troubleshooting
Lubrication, Maintenance and Tune-up
Engines: Twin Cam 88, 96, 103 and 110 cu.in.
Engine Top End and Exhaust
Engine Lower End
Clutch and Primary Drive
5-Speed Transmission 2006 Models
6-Speed Transmission 2007-2009 Models
Air/Fuel and Emission Systems (Carbureted Models)
Air/Fuel and Emission Systems (Fuel-Injected Models)
