Harley-Davidson Ignition Installation and Adjustment

A little theory
In a motorcycle engine, there are two fundamental systems that allow it to function: the fuel system, which provides the air-fuel mixture in the exact quantity and conditions required for proper combustion, and the ignition system, which produces the spark that will cause this combustion at the precise moment. The spark from the spark plug ignites the mixture, causing it to explode, and an increase in temperature and pressure in the combustion chamber (between the cylinder and the cylinder head) occurs due to the rapid expansion of the gases, which causes the piston to move.
It is very important that the spark occurs at a very specific moment so that the greatest expansion of gases occurs when the piston is at top dead center (TDC), to take full advantage of the explosion.

Since the piston moves up and down very quickly and the mixture needs a few milliseconds to burn completely, the spark must occur shortly before the piston reaches TDC, so that by the time it reaches this position, combustion has been as complete as possible. This is called "ignition advance." The advance varies depending on the engine's rpm and load. If the ignition is too far advanced, the gas expansion will occur while the piston is still rising, causing "knocking" or piston knocking, which can destroy an engine in seconds. If the advance is too far advanced, the engine will lose efficiency and our fuel consumption will be high. Later, we'll see how to adjust the ignition to its ideal setting.

Single Fire and Dual Fire
Simply explained, the ignition system has a magnetic sensor that picks up a signal when the crankshaft rotates, and therefore knows where the piston is. At the exact moment, it opens the coil circuit, and through it, a current is sent through the high-voltage cable to the spark plug, which produces the spark.
On Harley-Davidson models prior to 2000 (Sportster models prior to 2004), the coil produces a spark at both spark plugs simultaneously, known as Dual Fire. With this system, only one of the two sparks is used, as only one cylinder is ready for combustion at any given time.
During this period, aftermarket Single Fire ignition systems were produced, derived from racing, which only produce a spark from one plug at a time, resulting in more powerful ignition and more efficient combustion. This system is currently used on all HD models.

Let's get to work
We're going to install a complete ignition system, upgrading a Dual Fire system to the more modern and efficient Single Fire system. This system also has the advantage of being programmable, allowing us to choose various ignition curves, engine rev limits, pedal or electric start, and street or race use. Perfect!
The system consists of a rotor attached to the crankshaft, the electronic module with its adjustment plate, the coil and the high-voltage cables.

Installation is fairly simple. We start by removing the current system, following the service manual and the kit manufacturer's instructions. Next, we drill out the rivets on the sensor cover, remove the sensor, and replace the rotor with the new one.

We install and connect all the wiring following the instructions. It's very important that the connections are properly soldered and finished, as the reliability of our system depends on it.

Next, we place the ignition module in its housing and secure it with the two screws that will allow us to adjust it along the oval holes in the adjustment plate. After carefully reading the instructions, we use the switches to select the parameters (ignition curve, RPM limit, etc.) appropriate for our configuration.

Ignition adjustment
Now we move on to the most interesting and critical phase of the process: adjusting the ignition timing of our engine. To perform this task, we'll need a strobe gun (which emits a light each time a spark strikes the spark plug) and a transparent cap to view the ignition timing.

The first thing we'll do is remove the plug located between the two cylinder bases to see the crankshaft timing marks. It's important to know the exact timing marks for your year and model, based on the service manual.

After removing the spark plugs and engaging a gear, we turn the rear wheel until we can see the crankshaft TDC mark through the hole, and we center this mark in the window.

Next, we slightly loosen the bolts holding the ignition plate and slowly move it until the built-in LED turns off. At this precise point, the ignition is synchronized. We assemble everything and install the transparent plug in the inspection window. We start and warm up the engine, and raise the idle speed to a steady 2000 RPM. Next, we connect the strobe gun clamp to the spark plug wire of the front cylinder (it's very important that it's the front cylinder).

Next, we aim the strobe gun at the inspection hole. The gun will emit a flash of light at the same time as the spark plug sparks, and we should see the ignition advance mark on the window (refer to your manual for the exact mark). If we don't see it, we'll need to loosen the ignition adjustment screws again and move the ignition slightly until the mark appears centered in the window.

Conclusion
Once the mark appears in the window, our ignition is "timing," that is, synchronized with the piston movement. From then on, the timing will be automatically adjusted based on the curves programmed in the ignition software. We reassemble everything and go road test the bike, checking that it runs smoothly, accelerates well, and has power.

Frank Burguera

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