By: Allen Bishop One of the first, if not the first, bits of Ferrari lore that I ever learned was the admonition to keep your gold-plated screwdrivers away from the carburetors. The origin of this worthy piece of advice was said in a fit of annoyance by the late Luigi Chinetti, who was exasperated by American Ferrari owners who could not seem to resist the temptation to tamper with the Webers.
In the late 40's and early 50's, Ferraris were thin on the ground, particularly in the USA, and little technical information was forthcoming on them from the Factory or anywhere else for that matter. Many of our mechanics were certainly familiar with a set of three deuces (Stromberg 97s) on a hopped-up Ford or Merc Flathead V-8, but those were almost always set up to operated progressively, i.e., the engine ran off the center carb at low revs, the two end carbs "coming in" only when the "loud pedal" was floored. Hey, I grew up in street rod territory, and I remember how in awe I was when I realized that a "street" Ferrari's carburetors all opened at the same time! Unlike the guys with the gold-plated screwdrivers, I was scared stiff of the thought of messing with Webers. In fact, the first set of Webers I ever rebuilt was for a 250 Mille Miglia - the fabulous but problematical 36 IF4C four-barrels.
I would like to outline some of the checks and procedures necessary to tune and maintain the carburetors on Ferraris built prior to the Bosch fuel injection era. For a few moments, put down your gold-plated tools. No, I'm not going into the theory of carburetion, but there are some very critical functional checks that often are ignored, but are basic to correct operation.
First, the engine's ignition system must be in completely correct order. This is another topic altogether which I won't discuss in any further detail here, but it is primary to correct carburetor setting.
Next, all the linkage and cables from the pedal to the carburetors themselves must be correctly adjusted. Primary to this are the levers that push and pull the throttles open and shut. They must be exactly the same length or strange things will happen. The throttle return spring must have its tension set via the adjustable bellcrank to a reasonable level. These springs are an excellent example of Ferrari overkill; excessive tension can and will lead to needless and disruptive wear on the carburetors. These springs will pull a barn door shut!
Regarding the throttle pedal itself, there are two questions to be answered. First, when floored are the throttle plates wide open? Second, is the pedal's position essentially comfortable for your driving style? If you participate in track events, can you safely engage in heel-toe braking maneuvers? The pedal position is variable within certain limits and should be considered if your right ankle bothers you after a drive. Also, if your car is equipped with a throttle cable make sure it is in good working order, not ready to snap at 100 MPH.
Air filters have to come off for any but the most minor work and their condition should be verified. Dirty filters restrict air flow and will disrupt the air/fuel ratio at all RPM ranges.
Relative to the above; it was sort of chic to run road cars sans air filter a number of years ago, the carbs being fitted with Weber aftermarket "velocity stacks." These have to rate as one of the most useless decorations ever put on a V-12. Not only do they flow air poorly, but also they require a change in jetting which, of course, was never done. Furthermore, in the event of a blowback, they can allow a nice fire to start as well as under the best of circumstances allow all the dried paint and debris on the underside of the hood to drop right in for a friendly clogging. With the emphasis on originality over the past years, these little pieces of junk have largely vanished. The above remarks do not apply to those engines which were Factory fitted with stax, but these are full competition motors which were tuned for their use from the beginning.
The next item to check is the fuel system. Are the fuel filters clean? Are the fuel pumps delivering the goods? A mysterious loss of fuel flow can sometimes be traced to the yellow, wire-wrapped fuel hoses that Ferrari used for years. This tubing was originally designed by Salva for use in aircraft and warship fuel and lubrication systems. This stuff in almost indestructible and I lament its passing as OEM. However, when it really grows old, it can begin to deteriorate from the inside and clog the flow. Replacement line is available from several parts sources and is fairly simple to install. The new stuff is not quite as over-engineered as the older designs, but is still far superior to anything else I've encountered.
Finally, we arrive at the carburetors themselves. Whether equipped with 3 or 6 Webers, there are a number of checks to be made. Faults in any of these areas must be corrected before the carburetors can be expected to do their job properly.
First, and this is something that has caught me by surprise, but is well worth a check: are all the jets and emulsion tubes identical? Admittedly, it is unusual to find a mismatch, but once or twice I have encountered this. All Weber calibrated components are stamped with a number denoting a metric dimension (hole size). Not only have I found mismatched jets on one or two occasions, but in one horrible instance I discovered that the jets, while all stamped correctly, had been drilled out. This process used to be common practice among racers of a bygone age, but is completely out of place on a road car! Stick to the jetting specifications published by the Factory - they are in the Owner's Manual. Be aware that some Weber parts/jets are becoming almost impossible to find; in the case of the augured-out jets, I had to solder them all closed and carefully redrill them using a set of Weber jet drills. Price out a set of those sometime! Again, the aforementioned difficulties have occurred once or twice in nearly 20 years of Ferrari work, so I'm not trying to scare you, just be aware of any and all possibilities.
Now the common gripes. Since the mid-1950's, Weber has used die-cast alloys of several types for their carburetor bodies, covers, venturis, and diffusors. Some proved to be prone to corrosion and were painted a striking gloss black. The problem is that over a long period of heating and cooling, coupled with golden wrenches over-tightening them to the intake manifolds, the bases warp, allowing air leaks. I have found these carb bodies warped as much as .100 inch edges to center. Some have been packed with three or four base gaskets along with liberal application of goop in a vain attempt to achieve a proper seal. This situation can only be corrected by complete disassembly of the carbs and having a careful machinist mill them flat - AND perpendicular, not at a 5 degree angle!
The next one is tougher - worn throttle shafts and bores. The alloy bodies allow the holes where the throttle shafts pass through to wear oval; the shafts themselves being of brass are harder than the bodies. BUT they wear too. In times past, Weber provided oversize throttle shafts in a kit with a suitable reamer to bring all back to specification. No more.
This malady, when advanced beyond a certain point, will cause the throttle plates to mis-align when shut and leave ridges in the carburetor's barrels. One of two companies I know of can completely restore carburetors in the condition I have described. Cost? Don't ask.
The aforementioned situation applies to the 3-Weber setups; the DCN types have both throttle pieces on a common shaft that pivots on two small ball bearings, but note that some of the worst base warpits is found on the DCNs. Their 3-point base mounts seem to suffer this problem to a great degree.
You cannot attain a smooth, even idle and sharp acceleration/deceleration with the engine if the above problems exist, and it is as I have found a waste of time to try. Another situation that precludes proper idle and running adjustment is when the throttle plates have been removed from their shafts during a carb overhaul, and then not reseated concentrically in the bore(s). When this happens, there is an internal air bleed which permits excess air flow in the affected barrel(s). In the next installment I will outline the actual setting/synchronization procedures.
About the author: Allen Bishop owns Galloway Enterprises, a full service shop specializing in Ferrari maintenance and repair. Located in the Pacific Palisades, he has been working on Ferraris for more than 20 years. If you have any questions, feel free to call him at: 310-454-1904.