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MODIFYING

TBI-TO-CARB CONVERSION

For All CFI V6 & V8 Cougars and Thunderbirds
Revised September 7, 2016

Because the 1980's was an era of sweeping change as far as automotive electronics, our cars were caught smack dab in the middle of those changes at Ford. At the beginning of the decade, carburetors were still the norm; then we went through the transition phase (central fuel injection, or CFI); and finally by the end of the decade, sequential fuel injection (SEFI) became standard. The good news is, major objectives such as improved fuel economy and better emissions controls were achieved. The bad news is that horsepower did not significantly increase, a problem when the cars' weight also increases. If you own a 1983-87 V6 or 1983-85 V8 Cougar, you know this firsthand. Plus, with three different types of fuel delivery in just the aero Fox Cougars alone, it can be daunting sometimes to understand and diganose problems. Certainly if you're comfortable with a good old-fashioned carburetor, it would be nice to tune things that way.

If you're looking to ditch the stock CFI unit and pop on a carburetor, this is a great way to get back some needed power. Yes, you'll be bypassing some emissions controls but you can retain your EGR and PCV valve if that's an issue. The key here is not only to unlock some horsepower but also to keep the car driving great while still being managable.

You need good cylinder heads to start with for a carb to work properly, and right now if you have a 1983-87 3.8L V6 or a 1983-85 5.0L V8, then you have them from the factory. There are better heads to use but for early-to-mid 1980's castings, these are not bad at all.

T>he next step is finding a compatible lower intake manifold. Your stock intake (V6 or V8) will handle a 2-bbl carb just fine. On the 5.0L V8 side, if you want to throw on a 4-bbl carb, take your pick! A quick trip to Summit Racing or Jeg's online will net you anything you wish. Or you can use a 1979-85 Mustang 5.0 carb-spec intake. For the 3.8L V6 you'll need to hunt down the hard-to-find 3.8L carb intake, used in 1982-83 in the U.S. and up through 1984 in Canada.

1982-83 Carburetor

Next you'll need to find a carburetor. For a stock 5.0 with stock heads, anything over 600-650 cfms is going to be serious overkill. Really, if you're not planning any exhaust work, you can get away with a 600 cfm carb easily. Again, aftermarket carbs are plentiful at the places mentioned above. For the 3.8L, once again you'll need to hunt down 1982-83 parts.

Now the hard part: getting all the linkage set up and correct, installing a new distributor, tweaking the fuel delivery system, and installing the correct components for the ignition system. You will not be able to retain your EEC-IV components (1984-87) in the ignition system; you will have to revert back to the older but still usable Duraspark II system that Ford employed in the early 1980's. For 1984 models, you have two fuel pumps: a high-pressure and a low-pressure pump. You can reuse the low-pressure pump for your needs. For all other years, you will need to either install an aftermarket low-pressure (carb) fuel pump inline, or use a mechanical fuel pump (which requires an older timing chain cover). More information on the fuel system and all other details below.

Tim has written the great article below on how to do everything right on his '84 Thunderbird V8. Please note that some information is experimental, and some is from his opinion only. If you're going to follow the instructions, you will do so at your own risk and cannot hold Tim or this site responsible. Please see our disclaimer for more details.



"With a little ingenuity you CAN convert your 5.0 from the TBI EEC system to a 4 barrel carburetor and Duraspark II ignition without losing ANY of your convenience features, such as cruise control, or the use of your AOD transmission.

"I converted my 1984 Thunderbird 5.0 using a non-EGR Edelbrock intake (model 2121), a vacuum operated Holley carburetor, and a distributor for a carbureted 5.0 Mustang. I got the ignition module from the local salvage yard. I also got a ballast resistor from the parts store (needs to be 0.8 - 1.6 ohms). Most aftermarket books showing the ignition systems should have a decent representation of the ignition wiring.

"I used the existing fuel lines, ignoring the return line and the purge line, since without the TBI and EEC, there is nothing to utilize or operate them. How you hook up the fuel line to the carb is your choice. You can use rigid steel line, or adapt everything and use flexible rubber fuel line. Finally, find a 12" long 5/16" steel line with appropriate fittings and put it in place of your high pressure fuel pump. Then find the connector for the fuel pump relay in the right side kick panel near the computer and ground the tan wire. That will allow the low pressure fuel pump in the tank to operate full time. If you don't, the computer will turn it off because it won't sense any fuel usage.

"The only other issue is the TV rod for the AOD. After looking at the throttle Body setup, and talking to my local transmission guru, I determined that any mount point on the carburetors accelerator plate would be too close to the pivot point of the plate, reducing the travel distance of the TV rod. This was determined by trial and error, as my original connection was on the carburetors linkage plate, and the transmission wouldn't shift properly. I don't think I can give specific directions for this, so you must look at your original stuff and figure the best way to duplicate the linkage travel as best you can. I just fabricated an extension plate to mount the ball stud on, putting it out further from the pivot point, and that solved all my shift errors. Transmission works same as before, for which I'm pleased.

"Seems Edlebrock managed to include an adapter plate for the OEM throttle linkage bracket with their intake, model 2121, and with a slight tweak the original stuff mounted and fit nicely. Had to buy a set of ball studs for the throttle plate on the carb, a 600 cfm Holley vacuum secondary, then managed to put one in backwards for the AOD TV rod, reversing the grommet on the rod, which Holley said wouldn't work. They didn't design the throttle plate on the carb to work with the AOD tranny TV rod, but they told me the cable assembly used on the later models would work. Lokar makes one, and Windsor Fox makes a conversion kit, although theirs seems to require replacing the rod in the tranny, too. Not sure about Lokar's cable kit yet.

"One note of importance about the ignition wiring - you must cut the tach wire to the ECA, since the EEC system distributor signals the computer to produce the tach signal, and the Duraspark II system produces the tach signal at the distributor. If you don't disconnect the ECA from the tach signal, the tach signal from the Duraspark II distributor will be lost in the ECA, and the coil will never see it. Easiest way to do this is cut the tack wire just off the coil, and splice into it there for the ignition module.

"With a set of later model heads reworked for a nice top end overhaul, the Edlebrock intake and Holley carb, and the Mustang headers with dual exhaust all combined seem to have put me close to the 200hp range, because performance is way up."

 

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