Stromberg carburettor Auto water choke Overhauling

Stromberg carburettor Automatic choke Overhauling (water type) guide.

Note models may be different in side depending on age of carburettor also see Manual pull operated guide.

The choke flap is open during the operation of normal running and driving, In cold weather a much richer mixture is needed for cold starts.
When outside is cold so is the engine cold and the water in the system is also cold, the flap is held closed by a bi-metallic spring, controlled by water temperature. As the engine warms up, the water heats and the spring expands, closing the flap after years of service they can become corroded or worn.

1. First Disconnect the inlet and outlet water pipes from the water jacket on the choke unit. Undo the centre bolt and remove the water jacket hoses can be left in place if room and just checking, but be sure to check for cracks and wear on these especially round the fastening clips.

2. Depending on model remove the three screws and clamp ring as shown. Carefully remove the finned heat mass and coil spring check for damage and corroded dirty parts also inside the the water jacket top for blockage.

3. Remove the heat insulator. Clean inside the choke housing. Check that the metering needle moves freely. If not, prise off the choke spindle clip and remove the stepped cam, spring and thermostat lever. Undo the housing plug and remove the metering needle. Carefully clean the needle and reassemble it. Undo the three screws holding the piston cover.

Remove the cover and piston. check and clean the piston and refit it. Reassemble the lever, also check spring and stepped cam to the choke spindle before Reassemble and replace spring or parts if broken corroded or worn . Refit the retaining clip to secure them.

4. Rotate the thermostat lever anti clockwise. Use a feeler blade to measure the distance between the base of the stepped cam and the fast-idle needle. (Check the clearance) for the model.

5. Fit the heat insulator. Make sure that the peg on the thermostat lever fits through the slot in the insulator. Refit the coil spring and heat mass. 

Line up the marks on the heat mass, body casting and retaining plate. Fit the plate screws. Replace the water jacket and hoses.

Check for leaks  and top up if pipes have been disconnected re pressurise the system if coolant is lost and allow to get to temperature.