By the year 1932 when the first updraft carburetors were introduced, Carter already had vast experience in the automotive world. Founded in 1909, Carter Carburetor Company achieved several milestones that earned them the confidence of Chrysler and Plymouth as one of their trusted providers. That’s how the 1932 Chrysler DeSoto, as well as several Dodge and Plymouth cars, used Carter’s C1, SC, PB, and DL BB-1 carburetors.
Needless to say that Carter’s BB-1 design was a complete success.
Mechanics across the US quickly started using BB-1 updraft carburetors on older models and even fitted BB-1 units on engines other than Chrysler, Plymouth, or Dodge. That willingness to use BB-1 updraft carburetors brought Carter’s attention to the point of releasing in 1934 three “universal” BB-1 carburetors, the Carter 245S (SAE size 1), the Carter BB-1A (SAE size 2), and the Carter 289S (SAE size 3), as well as one prototype the Carter 263S (SAE size 4). According to Carter, the new models were better suited for upgrading vehicles regardless of their intake offset design. The automotive community's response was immediate. Larger units like Johnson and Schebler carburetors were replaced by the smaller and considerably better BB-1 design.
Carter’s dominance in this segment was undeniable. While it is true that Stromberg was also manufacturing BB-1 carburetors in the 30s their units didn’t offer the same advantages of Carter’s. First of all, Carter BB-1 carburetors were smaller which was a decisive factor for many applications. Secondly, and most importantly, the Carter BB-1 updraft design was more flexible. Their “universal” throttle shaft, that allowed the throttle arm to be fastened on either side of the unit, their adjustable main metering jet, their fast idle provision, and their multiple idle jets and main air bleeds available was a clear advantage over Stromberg’s. In other words, the Carter BB-1 could be installed on almost any engine, regardless of size. However, make no mistake, Stromberg’s carbs were excellent units, arguably preferable to Carter for some applications. Carter’s edge had to do with its “universal” design along with its awesome performance. That was the winning combination to make them the first option for most mechanics of that time.
Even though the Carter BB-1 carburetor provided significant advancements in the field of fuel supply, "conventional" carburetors continued evolving and improving. As mechanical fuel pumps became more and more common, downdraft carburetors took again the lead against updraft and side-draft carburetors. That explains why the Carter BB-1 was not used on more OEM applications but instead evolved as a niche product.
After World War II, Carter's BB-1 cast-iron lower bowl casting was replaced with a lighter zinc alloy casting as well as a revised 6-bolt body that prevented this new material from warping under the high temperatures of the intake manifold. The new universal models were renumbered as follows:
Carter 245S (SAE size 1) part number changed to 245SD
Carter BB-1A (SAE size 2) part number changed to BB-1D
Carter 289S (SAE size 3) part number changed to 289SD
Carter BB-1 reduced dimensions and mounting flexibility allowed it to be widely used well into the 60s on cab-over-engine Chevrolet and Dodge trucks as well as in marine, military, and industrial engines that only required to run at idle or constant revolutions for a prolonged period of time. Carter’s popularity allowed the manufacturer to release a total of 69 different carburetors under the BB-1 series, quite a feat considering their limitations when compared to other designs available in the 60s.
All in all, the wide adoption of downdraft carburetors was not only motivated by the popularity of mechanical pumps. Truth is BB-1 carburetors required (and still require) qualified personnel for its adequate service. It’s not uncommon, even among seasoned mechanics, to face “unexplained issues” when they are not familiarized with Carter’s design “peculiarities”.
Mechanical accelerator pump. Engines equipped with a Carter BB-1 updraft carb should be always started using the choke valve. This is directly related to the mechanical accelerator pump used by Carter on its BB-1 carburetors (arguably one of the worse design decisions taken by Carter engineers). Unlike conventional downdraft carburetors or updraft carbs with a vacuum-operated accelerator pump, when you attempt to start an engine with a Carter BB-1 unit, pressing the pedal several times won’t do any good. In most cases, fuel will end up in the exhaust system (since there is no vacuum that makes it go up through the intake). As you might guess, that fuel in the exhaust manifold constitutes a safety risk once the engine is finally started.
Idle circuit hidden jet. There is a small orifice concealed far down the BB-1's lower casting that holds the idle circuit jet. Experienced technicians like those who work at Mike's Carburetor Parts know that it is crucial to clean that little jet and clean the passage below it to prevent poor idle quality issues. We recommend not removing this jet without the proper removal tool, which is not available these days.
Replaceable power jet spring. Another professional tip from Mike's Carburetor technicians has to do with power jet spring fatigue. Most mechanics inexperienced with this type of carb do not replace this spring when servicing these units. Big mistake. The power jet spring supports great pressures and therefore it is mandatory to replace it during rebuilding. Failure to do so will not allow the power jet to settle into the valve and will remain constantly open causing a rich condition.
Stuck accelerator pump. We already mentioned the mechanical accelerator pump and the importance of using the choke. However, what we did not say was that the brass-made accelerator pump is prone to stick to the lower body when the engine is off for prolonged periods of time. To avoid damaging the case during disassembly, the best solution is to use a professional-grade ultrasonic cleaner, like the one Mike's Carburetor Parts has.
Last but not least, if you are shopping around for a good Carter carburetor then it would be wise to choose your retailer carefully. Buying from a reputable Carter specialist, like Mike’s Carburetor Parts, could literally save you time and money.
Carter BB-1 fuel valve orifice size. Unfortunately, in the 60s some auto part manufacturers didn’t pay enough attention to “little” details like properly identifying different applications. That was the case with Carter and the BB-1 fuel valve orifice valve. The BB-1 was manufactured with either a 0.101-inch orifice (intended for fuel pumps) or 0.118-inch orifice (intended for gravity feed applications). Carter used the same part number for both applications, meaning that your provider will be responsible for identifying them.