Owners manual

2 INSTALLATION INSTRUCTIONS
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FACTOR Advance Timing Retard Timing
For For
Cylinder Pressure Low High
RPM High Low
Vacuum High Low
Energy of Ignition Low High
Fuel Octane High Low
Mixture (Air/Fuel) Rich Lean
Temperature Cool Hot
Combustion Chamber Shape Open Compact
Spark Plug Location Offset Center
Combustion Turbulence Low High
Load Light Heavy
Figure 1 Ignition Timing Factors.
As you can see from the chart, most factors will change throughout the range of the engine operation.
The timing mechanism of the distributor must make timing changes based on these factors.
Example: An engine has 11.5:1compression, a high energy ignition and turns 5,500 rpm. With the
specifications given, you will have to retard the timing for the high compression, low rpm and high
energy ignition. By comparing the engine’s specifications against the chart, a usable timing guideline
can be found. Engines with a combination of items from both columns will require a timing that is set
in the mid range.
Obviously a full technical explanation of correct ignition timing would be very complicated. The best
way to arrive at a suitable ignition curve for your engine is to use the Ignition Timing Factors Chart
as a guide and compare it to the Advance Graphs in Figure 2 until a suitable curve is found. When
selecting your advance curve, use detonation (engine ping) as an indicator of too much advance,
and a decrease in power as an indicator of too little advance.
TIPS ON SELECTING AN ADVANCE CURVE
• Useasmuchinitialadvanceaspossiblewithoutencounteringexcessivestarterloadorengine
kick-back.
• Startthecentrifugaladvancejustabovetheidlerpm.
• Thestartingpointofthecentrifugaladvancecurveiscontrolledbytheinstalledlengthandtension
of the spring.
• Howquicklythecentrifugaladvance(slope)comesiniscontrolledbythespringstiffness.The
stiffer the spring, the slower the advance curve.
• Theamountofadvanceiscontrolledbytheadvancebushing.Thebiggerthebushing,thesmaller
the amount of advance.