The Zenith Stromberg Float Bowl Vent

Starting around 1973, British cars like Triumph TR6s and Spitfires started using Zenith Stromberg carburetors with a little brass tube coming off the side near the air cleaner. There's also a valve on the side of the carb body that invariably freezes up. So the question is... what the heck is this stuff and why do I need it? What it is is a float bowl vent. In the early 70s, charcoal canisters started showing up. At first, this was to create a closed system for the fuel. All modern cars use a similar system, and what's basically happening is that instead of having the fuel tank vent to the atmosphere, it vents into a charcoal canister. From there, the vapors are either returned to the fuel tank or drawn into the engine. Around 1973, Zenith-Stromberg carbs added a new float vent on the side of the carburetor so that the float bowl would vent to the charcoal canister at idle instead of the air cleaner. That makes the idle cleaner, which yeah... is an emissions thing, but it also makes it so you don't smell like a gas can after sitting in traffic. Everything in these cars was designed to work as a system, and it doesn't hurt performance as much as you'd think. In fact, most of the performance losses were due to toned down camshaft profiles and reduced compression in the engines. Bump up the compression, get some roller rockers, and put on a new exhaust header... and you might find that things like the float vent aren't the thing that's strangling your engine. I like to keep things as original as possible (up to a point... the air pump or the water choke would a different story). Hopefully, this video helps answer what that tube is for. If you need help rebuilding the carbs, distributor, or other components for your Triumph TR, Spitfire, GT6; or your Austin Healey, Mini, Jag or even your MGB... whatever British sports car you drive... check us out at www.midwestmotoring.com and ask if we can help!