Zenith-Stromberg and SU Carburetors Part II: Acceleration and Choke

In this video we take a deeper dive into how the cold start (i.e. choke) is accomplished in Zenith Stromberg CD and SU HS series carburetors. Also, as these carbs don't have an accelerator pump as with many other styles, how exactly do they create a temporarily richer mixture under acceleration? For most applications, I prefer rebuilding the original Zenith Stromberg or SU carburetors to replacing them with something like a Weber. Don't get me wrong--Webers are great carbs--but they're better suited to modified engines, and are unnecessarily complicated and temperamental on a stock setup. The problem with SUs or Zenith Strombergs is really just that they are misunderstood. They were actually a terrific choice for the Triumph TR, Spitfire, MGB, Austin Healey, Jaguar.... you name it. If the XKE used SUs, you can rest assured that you're definitely dealing with something that can be considered a "performance" carburetor. In actual practice, there are only 2 main downsides. First, by design they really don't work well in a down-draft setup, so apart from a few angled installations (such as the Triumph Stag) these will be a side-draft only carb. Second, the air valve has a shape that can restrict flow, so at wide open throttle a 40mm Weber is going to provide more flow than a 40mm SU every time. That said, a pair of Strombergs can easily provide plenty of flow for a Triumph TR6 engine, and are not the limiting factor in that setup. They're simple, reliable, easy to tune, and very flexible! I have other videos showing how to tune and rebuild them, and this multi-part video is intended to compliment those by helping you understand how they work in the first place. Enjoy!