Weber Carburetors and the 911
The last production year for Porsche cars using the Weber 40IDA3C type carburetor was 1972. The ongoing requirement to improve fuel efficiency and decrease air emissions (which was better achieved by use of EFI systems) heralded the end of carburetors on Porsche engines. This shift resulted in the decline of demand for triple throat Weber carburetors with a customer base consisting primarily of the limited production Lamborghini Miura, Ferrari 365BB & 512BB and Porsche 911 owners. Weber (Bologna, Italy) then focused their interests toward manufacturing fuel injection components and after acquiring the Carter Carburetor Company in Sanford, North Carolina the production of triple throat Webers was transferred there in 1979. This continuation of production continued through the early 1990s.
The first application for triple throat Webers as used by Porsche was in support of the 6-cylinder Porsche 901/20 racing engine and as such were designed by Weber specifically for this application. Six 904 GTS race prototypes (906; not 904/6) were outfitted with this engine in 1963. Carburetor testing using two of these 906s was conducted at Monza in December 1964; one used Weber 46IDA3C carburetors with 46mm throttle bores and the other used Solex 40PI carburetors with their throttle bores increased to 44mm. For the production version of the 901, Porsche developed the type 821, six-cylinder engine (predecessor to the 901 design) which incorporated Solex carburetors as was the typical selection for their production engines. These Solexes were specifically redesigned for the type 901/01 engine (becoming the Solex type 40PI); three being mounted on a common intake manifold with a single, integral fuel float bowl; two sets per engine. The first production 901 cars (later renamed 911) introduced in 1964 used the 40PI carburetors but Porsche later abandoned the 40PI due to their short service-life and associated tuning issues; their replacement with Webers started in Feb 1966 and continued until replacement with MFI fuel delivery systems.
Prior to Porsche adopting them for use on the 911 in 1966, Webers were only used on their dedicated racers beginning with the 550 Spyder and continuing with use on prototype and GT racers through the early 1970s. Their development for the 906 engines in 1964 explains how Webers were readily available for the production 911 in February 1966 after the Solexes proved troublesome in service.
It is interesting to note that Weber did produce a series of triple throat carburetors used by the Ferrari "Sharknose" 156 F1 cars of 1961 which were 40IF3C but these carburetors used a dedicated float bowl for each throttle bore while the Porsche triple throat Webers used only two bowls for the three barrels. Also of interest is the claim that the 40IDA3C Webers were first used on the Lancia Aurelia V6 in the mid-1950s but that engine actually used a either three twin-throat Webers or a single Weber carburetor feeding all six cylinders.
In service for decades, the Weber 40IDA3C carburetor has provided exceptional performance for six cylinder Porsches, Ferrari BBs, Lamborghini Miuras (debuted at the Turin Salon in December 1965), Renault Alpine A310s, Chevrolet Corvairs, three cylinder Saabs and other applications. Demand for these carburetors remains strong as enthusiasts choose to replace their CIS or MFI equipped engines with the less complicated Webers. However the use of these triple throat Weber carburetors is dependent upon their being in excellent condition mechanically and then well matched for their intended application. No longer manufactured, these carburetors are typically at the end of their service life and are scarce to find in decent condition. Fortunately they may be resurrected by careful remanufacturing and tuning to provide performance and reliability equal to or exceeding that of new carburetors.
As an alternative to Webers, PMO carburetors were developed by Richard Parr and became available starting in 1997; they fill the void of new carburetors and provide design improvements for enhanced performance. PMOs are excellent products but they are not Webers. Webers enjoy a long and rich history and demand respect as such. Cars originally equipped with them must retain them for originality, other enthusiasts prefer the pedigree or appearance of Webers over that of PMOs; and as good as PMOs are; the Webers are excellent performers if in good condition.
Zenith triple-throat 40TIN carburetors as used on the 1970 and 1971 911T engines and the earliest Solex 40PI carburetors with their recirculating overflow fuel systems as used on the 1964 through 1966 engines have seen interest in applications on the 911 engines either from originality for the early cars or for lower initial cost in the case of the Zeniths. All carburetors differ in individual details, however; they all share basic similarities and regardless of design variations they will all provide a multitude of poor engine performance troubles due to incorrect tuning, worn-out components and due to jetting errors.
Although the triple throat 40IDA3C type throttle body appears complex it is really nothing more than three separate single throat carburetors and two fuel float chambers combined into one housing or throttle body. Each throat incorporates discrete fuel delivery systems to provide for all ranges of engine operation.
The most typical complaint about Webers is that they are finicky: this is true if they are old (defying adjustment due to wear issues) or are not adjusted properly (a surprisingly large percentage). Certainly PMO carburetors, mechanical fuel injection or electronic fuel injection systems have attraction over worn-out Webers for convenience or performance; choose your poison and embrace the challenges and uniqueness of your fuel delivery system selection: an enthusiast’s car has personality associated with its intrinsic demands.
there is little argument of Weber carburetors deserving their reputation as the finest high performance carburetor available, grateful thanks to Eduardo Weber.