Journal: Scot Abbott's Journal

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I built a GT6 spitfire for my son and converted the twin carb 2 liter motor to fuel injection. It was my very first project in that area. The fuel injection conversion process had 4 main parts:

adapting the carbs to hold fuel injectors
adding a high pressure fuel system with regulated pressure
setting it up for computer control
Tuning it to run

Part 1 Adapting the carbs


The carbs can be adapted for EFI by adding holders for the injectors, and retaining the main carb structure to act as a TBI. The first holders add holders from the top of the carb, and are quick, easy and reversible. The second type of adaptation puts the holders underneath the carb body-and essentially HIDDEN. This second type of conversion does require modifying the carb bodies. It is shown in some detail on page 3 and 4 of this journal.


HOLDERS WITH INJECTORS ON TOP:

(On these first holders I cut out a small part of the back center part of the carb to give the best possible angle for the injectors. I later found that cutting out the back slot in the carb bodies was not necessary)

The first adapters to hold the fuel injectors in place were made out of copper sheet and copper tubing. I used household scissors, a propane torch, a bench vice, a hacksaw and an electric drill. In the first step, I made a pattern out of masking tape which conforms to the inside of the top part of the carb. I used it to cut out the copper liner piece as shown in the picture below. A later design which works as well is given on page 2 or 3 of the journals, and it doesnt even require soldering.

Figure 1

I next pressed it it into the top of the carb so it would conform to that shape.

Figure 2

Once this was done, I soldered the ends of the coper piece together so the piece was fairly rigid. I did this in while the piece was sitting on a vice. I used a small propane (bernzomatic) torch. I could have done it in place in the carb body, being careful not to over-heat melt the piece. (I did this later and had problems.)

Figure 3
I then soldered a couple of small pieces of 1/2" copper tubing in place to hold the injectors so they would squirt directly at the back of the throttle plate.
For the gt6 carbs I cut out a section of the top cap mounting surface, leaving the screws in place for later mounting. In retrospect, I found this was not necessary.
I drilled the copper insert so the holes which which are used to hold the 'dome' on could be used to hold the adapter plate in place.


I recently have made some adapters like this which do not require cutting the back of the carb and they seem to work just as well. I had originally cut out the back so the injectors would have perfect alignment with the center of the throttle plate. This level of perfection is not required, I have now found. The new pattern is very similar to the old one but there is just two cuts on the sides rather than a cutout to clear the carb ears.
The newest 'from the top' does not require modifyong the carb body at all and it uses a simple injector holder. See the next pages of the journal for a drawing and details.

ADAPTATION WITH THE INJECTORS HELD UNDERNEATH THE CARB

This approach requires removing the float setup frtom the carb body and then making a passageway for the injectors. It can be done fairly neatly using a drill and file. It can be done very neatly using a die grindeer or a router.