EFI to carb conversion procedure - Defender Source
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Old May 3rd, 2013, 11:46 AM
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Rick Thompson
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EFI to carb conversion procedure

This is for a 94 NAS 3.9L I purchased everything from summit racing and my local Napa. You need the edelbrock rover manifold, #1404 carb, edelbrock banjo fitting for the carb, low press. fuel pump or a fuel pump regulator ( i used a mallory unit ) universal throttle cable, universal throttle cable mount, throttle return sping, choke, either manual or electric, and the water outlet fitting for the back side of the manifold to the heater, you need to either fab one or get one from Rimmer bros ( i did ) or RPI. Also, you need about 6' of heater hose and fuel line hose. you can re-use the stock water inlet/thermo housing. finally, some vacum line plugs and a valley gasket.

First remove the drain out a gallon or so of coolant, pull off the plenum, maf, air filter canister, wiring harness for the ecu/efi etc. Then it is pretty straight forward. Install the manifold per the instructions. Now, on the front of the manifold where the thermostat goes is a water bypass which you really do not need. I simply used a tube thread tap and tapped it to accept the plug that came installed on the back vacum port on the carb ( that port will later be used for the brakes) to block it off, use sealant and thread it in to where it is flush with the surface of the outlet, now you can put on the factory thermo housing on.

Then I put on the carb, you need a fitting for the rear port on the carb to hook up the brake master vacum to the carb. The front middle port gets blocked off and so does the small port on the drivers side. The small port on the passenger side goes to the vacum advance on the dizzy. For a nice pic of this, go to RPI's site. I next put on the throttle linkage, return spring and cable after removing the factory unit. To mount the manual choke cable ( i am switching to an electric choke, i started off with the manual just to get it all running at first ) i used some 16g metal and pop riveted it with rtv sealer to the fire wall right above the bonnet release.

I mounted the fuel pressure regulator where the factory air canister was for simplicity sake, i may move it later to clean thing up. Plumb it in as per the instructions. I picked up a fuel pressure gauge ($17) from O'reilly's to set the fuel pressure. For the return line on the regulator, i tapped into the return line by the tank and ran it to the fuel filler vent as a temporary return. There is too much restriction in the return line in the tank to get the fuel pressure to drop down to 5.5 psi. When I drop the tank, i will address this so that it uses the factory return. I just did this for now to get it running and I really dont see the problem, but I am changing it later just because. I hooke up the lines to the regulator and the port going to the carb I plugged it while I was setting the pressure as to no accidentally damage the carb with to much fuel pressure.

The plug that goes from the fuse panel/dash that plugs into the ECU i clipped off and put female connectors on the brown, white/red, white/purple wires to plug into the relay used for the fuel pump and then grounded it to the bulkhead and mounted it there for now.

Finally i hooked up the heater hose and used a push in filter for the valve cover at first to get it running but have since plumbed it into the air filter. The hose from the charcoal/evap cannister i tucked under the wing for now. You can plumb it into the carb but it requires drilling and tapping on the carb and will happen later. On the radiator the hose next to the hose to the expansion tank gets removed and blocked off. The two front air/fuel screws i turned in and backed out 2 turns IIRC. (RPI's site has the instructions).

So far it has been running great. I do notice the increased torque from it. I have had to tinker with the idle to get it just right. So far the jetting seems right on. Some sites reccommend going down a size on the mains and the metering rods but I have headers into a single cat with 3" pipes.

I was pretty easy to do and hopefully i did not leave anything out. And for everyone wondering why I did it, I was tired of chasing gremlins. I like simplicity. I like how it runs now.
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  #2  
Old May 3rd, 2013, 11:52 AM
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evilfij
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When you do drop the tank, I would consider pulling the factory pump and using a low pressure pump (like the original 3.5 V8 carb rovers) mounted outside the tank. You can convert the factory pump to a pickup and return just like the diesel conversion guys do. I can't see the factory pump being too happy being regulated down to 5.5psi, but what do I know.
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Old May 3rd, 2013, 12:00 PM
wantone
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Rick Thompson
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I just replaced the pump a couple of months ago. With the regulator, it has a return line back to the tank so the pump is only pushing 5.5psi instead of the usual 35psi (?) If had the tank out when I did this, I would have just gutted the tank parts and put an inline pump.
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Old May 3rd, 2013, 12:21 PM
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what does this do legally, considering most OEM emissions have been removed?
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Old May 3rd, 2013, 12:26 PM
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Bill Adams
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IDK about NE, but in MD they only check to see if the gas cap is present. If pre OBDxx, they do a sniff test with an exhaust probe. A pass is a pass regardless of fuel induction.
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Old May 3rd, 2013, 12:39 PM
wantone
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Rick Thompson
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here in NE, there is not any inspection except when it first gets plated in the state. when they do that, they just check the vin, headligts and taillights.
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