Tech Tip: European Intake Manifold Conversion

Editor's Note: In the course of converting my GTV from the original SPICA manifold to a European, made-for-carbs model, I searched high and low for information and advice. Fellow ARCC'er George Beston was extremely helpful, as were other alfisti, but I was surprised that I hadn't come across the complete procedure detailed anywhere (on the internet or elsewhere). It turns out I just needed to go back in time to find it. This article appeared in the May 1984 issue of the ARCC's own Alfista magazine. I found it to be so thorough and helpful that I thought other members contemplating this sort of work might find it useful as well.

In a previous article, I dealt with the comparison of carburetors versus Spica fuel injection. A purely objective analysis of the numerous trade-offs didn't produce a decisive advantage for either system. While I personally prefer carburetors, I tried to point out that the Spica unit is very good, as well as being reliable.

I concluded that the real attraction of carburetors has to do with their effect on the Alfa's personality. They provide an elusive quality of "sparkle" that European drivers can still take for granted, but Canadian owners haven't enjoyed since the last carbureted Alfas were sold in '71. Twin side-draft carbs also have in aesthetic value, which may or may not turn you on. If you've decided by now that this is all a lot of nonsense, you're probably happy with your injected Alfa, and I strongly encourage you to leave everything just the way it is. Also, you won't need to read the rest of this article, because it concerns the technical details of carb conversion.

Now that we've narrowed down the audience a bit, let's start talking hardware. There are two completely different approaches to carb conversion: 1) install a pre-packaged kit (sold by Shankle, Bobcor, etc.) that adapts the existing fuel injection manifold and linkages for carburetor mounting, or 2) strip everything off and install all European components. This article concerns only option 2. Option 1 is a much easier way to go. There's no need for a tech article about it, because the kit will supply all the instructions you need.

Option 2 is for purists. If you go this route, you'll have to scrounge parts, improvise, maybe even fabricate. There are no rules or detailed instructions. I can't give you a complete procedure because the job will be different for each car. I'll try to cover the major points that should be common to all conversions, and include certain pitfalls you should know about ahead of time.

The major parts you'll need, beside a pair of carburetors, are: European carburetor intake manifold (2000 or 1750, depending on your engine); carb mounting blocks & gaskets; complete throttle linkage assembly including actuating rods, bellcrank, fittings, etc.; fuel injection pump block-off plate; low pressure fuel pump and regulator. There are lots of additional odds and ends you'll need, and I'll mention some of them as we go along. Now let's disconnect the battery ground cable and get started.

1. I recommend replacing the throttle linkage assembly first because that's the trickiest part of the whole job. If you can't get past this one, you can abort the project before any major disassembly has been done. Remove the gas pedal, throttle cable, return spring, hand throttle, and the two U-clamps that mount the linkage to the firewall. Now, remove the linkage from the car. At first you will be absolutely convinced that it can't be done without pulling the engine. Well, it can, but you're going to have to work at finding just the right orientation for it to come free. Installing the new linkage is almost as bad. Also, you may find that the vertical hand throttle lever collides with your brake vacuum booster. You may have to bend, or even saw it to eliminate this interference.
2. The next step is to remove the Spica injection pump. Pull off the drive belt and remove the 4 injector pipes from the pump. You have to start at the rear and work forward to get the compression nuts off. Remove all the FI Pump mounting supports, thermostatic actuator, hoses, linkage, etc. The easy way to pull the pump is to separate the upper and lower halves by removing six 1Omm nuts (you'll need a 10mm ¼" drive socket with a long extension). Once the upper part of the pump is out, you can easily get at the block mounting nuts on the lower part.
3. Install a block-off plate where the FI pump was. You'll have to buy one, make it yourself, or have it made. It should be at least ¼" aluminum milled for flatness. Use a gasket for a pattern.
4. Drain the radiator and disconnect all the hoses, wires, etc. running to the intake manifold. Remove the manifold and butterfly assemblies as a unit. The lower three nuts are tough to get at. You'll want a 13mm swivel socket. It may help to remove all the injector pipes first.
5. Now for an unpleasant surprise. You have to replace the upper four intake manifold mounting studs in the cylinder head. And if you're unlucky enough to have any frozen studs, you might end up pulling the head to install heli-coils. All these upper studs are too long. The outer ones don't have enough thread for the carburetor manifold; the inner ones bump into the carb mounting blocks. (The lower three studs are OK.) If you can remove the studs without damaging them, reinstall the two inner studs in the outer positions. Obtain two new studs, identical to the lower ones (37mm, Part No. 2100.05194 for the middle positions.
6. The 4 rubber carburetor mounts and the bellcrank should be securely fastened to the carburetor manifold. Clean up the head surface and install the manifold with a new gasket. Install the thermostat and all hoses, etc. Your old thermostat bypass hose won't work. The carb manifold requires a special, convoluted bypass hose - Alfa part No. 105.48.01.628.02. Replace the coolant.
7. Mount the two carburetors, being sure to get the interacting levers meshed properly. Don't forget to use a ground strap between the carbs and manifold to bridge the rubber mounts.
8. Install the carburetor actuating rods. The European set-up uses ball & socket connectors on the rods. The plastic fuel injection rod ends are better, and fit perfectly. In fact, I recommend using the long linkage from the Spica system itself as the actuator between the main throttle linkage and the bellcrank. To adjust the linkage you must alter the lengths of the two rods and the position of the mushroom-shaped stop under the gas pedal. At idle the butterflies should rest against the idle adjusting screw, and at full throttle they should be parallel to the barrels.
9. Replace the stock fuel pump with a low-pressure pump. I recommend the electronic "Facet" pump that retails for about $30. It's quiet, reliable, and efficient. You should be able to devise a way to mount it on the brackets holding the existing pump. You can retain the stock FI fuel filters and the fuel supply line. The fuel return line can be removed, and its inlet to the tank is then plugged. Install an in-line pressure regulator in the hose between the main filter and the front carb, and set the pressure for 3 psi.
10. Choke installation is pure improvisation, depending on what car you have. Most people use the hand throttle pull to activate the choke. The choke cable is difficult to install on Webers because the fittings are tucked so close to the manifold. With Dellortos, it's easy.
11. There are many different options for air filter assemblies. Whatever you use, you need some way to fasten the two carbs together at their intake ends, so they won't flex relative to each other and throw off the airflow balance. If they're both bolted to a European airbox, there's no problem. If you're using individual Filtron elements, you should fabricate a strap to tie the carbs together. Finally, the airbox or strap should be bolted to a strut that attaches to the right engine mount. This keeps everything rigid.
12. It's a big thrill when the job is all done and you're ready to start the car for the first time. Have a fire extinguisher handy so the thrill won't be more than you want. This isn't meant to alarm you, but you don't want to take any chances after all this work. The trouble with tuning a new carb installation is that the engine must be running to do it - but it won't start unless it's fairly close to the proper adjustment. You'll have to read the manuals for your carbs, and experiment, until you get it running. There are many ways to adjust twin side-draft carbs, but the UniSync + Colortune method is so superior to all of them that I wouldn't consider anything else.

I hope I haven't made the job sound more complicated than it really is. As I said before, I've done it twice, and both times it was the most enjoyable Alfa project I've ever worked on. I have two relatively late model Spiders, a '76 and a '79. (Don't ask me to explain why, because I can't. Let's just say I really like Alfa Spiders and leave it at that.) By 1980, both cars had been modified to provide all the performance I wanted from them: European cams, two-piece headers, electric cooling fans, and removal of certain -unnecessary- components. But then I began to get a little bored having two cars with the same mechanical set-up. I have always admired and coveted twin side-draft carbs, so I decided to do a European Weber conversion on the '76 (fully intending to leave the injected '79 alone). I was delighted with*the change - so much so that I started to look at the '79 with a jaundiced eye. A year later I converted it too but with Dellortos instead of Webers.

What about the difference between Dellortos and Webers? They both give an Alfa that intangible sparkle, but they each have personalities of their own. Webers are "hairier", Dellortos are much smoother and more refined. The choke action on the Dellortos is far superior, and I think they're a bit prettier to look at (of course, they don't have that distinctive wing-nut on top). My '76 Spider, with its rubber floor mats and minimal sound insulation, is what I like to call a "bare bones- sports car, and is better suited to the Webers. The '79 is a lot more luxurious (it even has carpets), and the Dellortos are a better choice. If I had all of this to do over again, I wouldn't change a thing!