TR8 Auto Choke

TR8 Auto Choke Issue

I recently solved a long-standing problem with the auto choke on my TR8, and I’m sharing this in case it helps anyone else experiencing similar issues.

The problem was puzzling: the auto choke would come on, but only after the engine had fully warmed up during a run. For a long time, I couldn’t understand why.

It turns out the issue lies inside the auto choke mechanism. There’s a small plastic pivot component with a series of fine teeth. As the engine warms up, a bi-metallic coil gradually rotates the mechanism, allowing the extra fuel enrichment to step back one tooth at a time until the choke is fully disengaged and locked in the “off” position.

However, in my case, the teeth on this plastic pivot had worn down over time. Without properly defined teeth:

• The mechanism cannot lock into the fully “off” position, so the choke remains partially engaged.

• It also won’t activate correctly when you depress the accelerator, because it can’t lock into position until heat from the engine moves the spring — at which point you don’t want the choke on anyway.

After around 40 years, wear like this is hardly surprising and may well explain why some owners find their choke staying on longer than it should.

Fortunately, I managed to source some NOS Stromberg carburettors from a Land Rover fitted with the same auto choke system. This made it possible to swap out the worn components without removing the carbs entirely — a bit fiddly, but perfectly doable.

For reference:

• Green pivot – Original unit with worn teeth

• Yellow pivot – New unit with sharp, intact teeth

The video clip shows how the teeth should properly engage during operation.

If your auto choke seems to have a mind of its own, worn pivot teeth may well be the culprit.