Harley-Davidson: EFI injection conversion to step by step

In this article we will materialize the dream of the most faithful followers of the Old School: we will eliminate the injection system (EFI) of a Twin Cam Harley-Davidson and we will change it for a carburetor, so that everything is again “as before”.
First of all, I want it to be clear that the modification has been made purely for experimental and aesthetic purposes, guided by nostalgia, since there was no real need that justified the change in this case: the injection worked perfectly and the engine rolled without problems , although it can serve as an example to those who wish to perform the replacement to eliminate malfunctions or defects of the system, such as Magneti Marelli injections with enough kilometers and erratic operation.

SPECIAL ENGINE-Special Carburer
To start we will review the list of 3 elements that we need to completely eliminate our EFI Injection System:
-Carburetor With your intake.
-Gasoline tap With its adapter.
-Compatible ignition module.
We start with the carburetor: as in our case the engine is a 100CI screamin 'eagle model with a lot corner.

The main modifications consist of a new machining of the interior of the venturí, the installation of a circular diffuser or “booster” and the addition of 2 Thunderjet circuits. These circuits come into action in high demand, and have an effect similar to an extra acceleration pump, which will catapult us towards infinity.

The gas tap and its adapter have been selected from the pingel catalog, products known for its high performance and reliability.

The ignition must be compatible with the sensor de rotación de cigüeñal original, este sensor será el único que se reutilizará del sistema de inyección.

This magnetic sensor will indicate in a very precise way the position of the pistons, so that the spark plugs emit the spark at the precise moment. We have used the Motmann Motonn Ignitions P3 system, very reliable, of simple installation and at the same time compatible with the original coil and the HD security system.

Disassemble!
Now that we have all the components we go with the funniest part: we will eliminate sensors, cables of admission, switchboard and any element of the EFI system (except the crankshaft position sensor as we have mentioned above).
After removing the fuse from the injection pump (important to consult the workshop manual throughout the process) we will try to start the engine to remove the pressure from the injection pump.

Después desconectaremos el borne negativo de la batería y desmontaremos el tanque de combustible, tras lo cual ya podemos desinstalar el módulo de inducción EFI.

Then we will open the gate at the top of the deposit,

para poder extraer la bomba de inyección, soltando a su vez el manguito de alta presión, lo que nos permitirá extraer la toma rápida del tubo de combustible.

Hacemos una pausa
Congratulations, we already have almost half of the work done! Antes del montaje de los nuevos componentes nos centraremos en desmontar todos los sensores y cables del sistema que ya no vamos a utilizar, para ello podemos echarle un vistazo a los diagramas de cableado que aparecen al final del manual de taller, de este modo volveremos a tener un sistema eléctrico muy simplificado y práctico, además de mejorar los resultados estéticos.
Es hora de tomar un descanso para repasar todo lo que hemos hecho y prepararnos para el siguiente paso, el montaje.

Instalación del carburador

We will continue to complete the “Downgrade” or conversion of an EFI electronic injection system to a carburetor system. In the first part we had listed the new elements and disassembling the components that will be removed, we only have to disassemble the escape O2 sensors and replace them with a plug, now we start the assembly.

The fuel tank
To resume the project we will start with the simplest part, after closing the upper gauged gate will install the fuel tap adapter and the tap, using a little teflon or liquid sealant so that there are no fuel leaks.

 

The admission
We begin with the intake or multiple take, as always following the instructions of the workshop manual and the manufacturer of the component we will install it “loose”, we will locate the carburetor in its final position with the help of its support and we will tighten the screws of the taking of the taking admission, marking its position to verify that it has not moved. Now we can disassemble the carburetor and re -apprehend the specified values, always trying that the shot does not move from its position, in this way it will remain totally aligned with the carburetor and no air leaks will occur in the admission.

Then we install the carburetor, support and air filter, in this case we have chosen a Machine performance element to enhance aggressive aesthetics at the same time that we increase the benefits.

In the following photo we can see the location of the 2 Thunderjet diffusers and their shots in the carburetor tank.

The ignition
The ignition installation is very simple if we follow the instructions, we must only connect the positive, negative, coil and crankshaft position sensor.

We will choose the location of the module in a sheltered site of the elements and the rain (for example under the seat).
It is important not to run and make the connections and location of the wiring as well as possible, remember that 90% of the electrical failures in the engines are due to defective connections.

After this we can already select the positions of the 3 dials of the ignition module, where we will choose the advance (green) and its type (yellow) and the RPM (red) limit.

Final tests
Once with the carburetor, ignition and electrical system in place we will proceed to assemble the gasoline tank on the motorcycle, connecting our new tap with the carburetor with an adequate fuel tube.
We connect the negative battery terminal and we can start the engine, we will check that everything works correctly and we will proceed to its adjustment.
Tech Tip: In the case of the S&S and CV carburetor (original HD) is adjustment, the engine is slightly heated and the idling screw is tightened until you get about 1000 rpm. Then we slowly close the mixing screw until the engine begins to fail, and memorize this position. We open the mixing screw again until the engine begins to fail again and memorize the position. The ideal adjustment is approximately among the 2 positions, we do it and just justice the idle at about 850 rpm. Voilà!
We can already put the helmet and go to the road brand new the new way of breathing of our beloved Twin Cam (Figure 10), we will verify that although the power is similar, the way to deliver it is more “raw” and the motorcycle no longer asks permission to accelerate, just do it!

Frank Burguera

#mecanicaharley