Installation and fitting of Harley-Davidson ignition

A little theory.
On the motorcycle engine there are 2 fundamental systems that allow the operation of the motorcycle: the power system, which provides the air-gasoline mixture in the exact quantity and conditions for good combustion and the ignition system to occur, which produces the spark that will cause this combustion at the precise time. The spark of the spark plug burns the mixture, this explosion, and an increase in temperature and pressure occurs in the combustion chamber (between the cylinder and the cylinder head) because the gases expand rapidly, causing the piston to move.
It is very important that the spark occurs at a very concrete time so that the greatest gas expansion occurs when the piston is at the top deadlock (PMS), to make the most of the explosion.

As the piston goes up and down very quickly and the mixture needs a few milliseconds to burn completely, the spark must be produced a little before the piston reaches the PMS, so that when the piston reaches this position a combustion has occurred as complete as possible. This is called “advance of the ignition.” The advance varies depending on the revolutions and the engine load. If the ignition is very advanced, the gas expansion will occur when the piston is still rising, causing the piston to “snack” or hitting, something that can tear a engine apart in seconds. If the advance is very late, we will lose engine efficiency, and our fuel consumption will be high. Then we'll see how to adjust the ignition at its ideal point.

Single Fire and Dual Fire
Explained in a simple way, the ignition system has a magnetic sensor that catches a signal when the crankshaft rotates, and therefore knows where the piston is located. At the exact moment, the coil circuit opens, and through the coil a current is sent through the high voltage cable to the spark plug, which produces the spark.
In the Harley-Davidson models prior to 2000 (pre-2004 Sportster) the coil produces a spark at a time in the 2 spark plugs, which is known as Dual Fire. With this system only one of the 2 sparks is used, as only 1 cylinder is prepared for combustion at each time.
During this time, aftermarket Single Fire systems were produced, derived from the competition, which only produce spark in 1 spark plug each time, making it more powerful, and combustion occurs more effectively. This system is currently employed on all HD models.

Let's get to work.
We will proceed to install a complete ignition system, to update a Dual Fire system to the most modern and efficient Fuego único. This system also has the advantage of being programmable, so we can choose several ignition curves, engine revolution limit, pedal or electric start and street or competition use. Perfect!
The system consists of a rotor attached to the crankshaft, the electronic module with its fitting plate, the coil and high voltage cables.

The installation is quite simple, we start by removing the current system following the service manual and instructions of the kit manufacturer. Then we drill the rivets of the sensor cap, remove the sensor cap, and change the rotor to the new one.

We install and connect the whole wiring on instructions, it is very important that the connections are well welded and finished, because it will depend on the reliability of our system.

Then we place the ignition module in your accommodation and hold it with the 2 screws that will allow us to adjust it along the oval holes that the adjustment plate carries. After carefully reading, we select the switches with the switches the parameters (ignition curve, RPM limit...) suitable for our configuration.

ignition adjustment
We are now going with the most interesting and critical phase of the process, where we will regulate the ignition advance of our engine. To accomplish this task we will need a strobe gun (emites a light whenever a spark occurs in the spark plug) and a transparent stopper so I could see the advance mark.

The first thing we'll do is remove the stopper between the two bases of the cylinders, so we can see the crankshaft advance marks. It is important to know what the exact marks of our year and model are, based on the service manual.

After we disassemble the spark plugs and gear a march we turn the rear wheel until we can see through the hole the mark of the crankshaft PMS, and we focus this mark on the window.

Then we lighten up the screws that hold the ignition plate and move it slowly until the LED that is built in is turned off. At this very point the ignition is synchronized. We set everything up and install the clear stopper in the inspection window. We ripped and warmed the engine, and we idled up to about 2000 stable RPMs. We then connect the stroboscopic gun clamp on the front cylinder spark plug cable (very important this cylinder is).

Then we focus the strobe gun on the inspection hole. The gun will emit a flash of light at the same time as spark of spark plug occurs, and on sale we should see the mark of ignition advance (see manual to find out what this mark is like). If we don't see it, we have to loosen the ignition adjustment screws again and move it slightly until the mark appears centered on the window.

Conclusion
Once the mark appears in the window we already have our “cale” ignition, i.e. synchronized with the movement of the piston. From there the advance will automatically be adjusted based on the programmed curves in the ignition software. We ride everything again and we're going to try the motorcycle on the road, checking it smooth wheel, speed well and it has power.

Frank Burguera

#mecanicaharley