2

INSTALLATION INSTRUCTIONS

Figure 2 Ignition Timing Factors.

Note: It is recommended to have a dial-back timing light, timing tape or a fully degreed balancer to

set the timing correctly.

CHOOSING AN ADVANCE CURVE

The function of the advance curve is to match the ignition timing to the burning rate of the fuel with

the speed (rpm) of the engine. The piston is traveling much faster through the combustion stroke at

5,000 rpm compared to 1,000 rpm. Any factor that changes the burning rate of the fuel or the engine

speed can cause a need for an ignition timing change. Figure 2 shows some of the factors that will

affect engine timing.

FACTOR

Advance Timing

Retard Timing

For

For

Cylinder Pressure

Low

High

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

As you can see from the chart, most factors will change throughout the range of the engine operation.

The Digital E-Curve allows you to make timing changes based on these factors.

Example: An engine has 11:1 compression, a high energy ignition and turns 5,500 rpm. With the

specifications given, you will have to retard the timing for the high compression 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 3 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. Also consider how the engine cranks and

starts. Too much advance can cause an engine to crank slow or even kick back. Here are a couple

of suggestions.

• Useasmuchinitialadvanceaspossiblewithoutencounteringexcessivestarterload.

• Starttheelectricaladvancejustabovetheidlerpm.

• Selectanadvancecurvethatproducesgoodaccelerationwithoutdetonation.