We now have available new AUC 8160 bodies for thermostatic choke units. These originally were cast and then machined, however due to the prohibitive cost of retooling, our in-house machine shop has modelled this to be machined from solid aluminium billet.
This was done on our 5 axis CNC in 2 operations before being laser engraved with the SU logo. To then give the bodies a more cast finish they have been rumbled in a soft bead medium to match the carburetter bodies. By manufacturing the bodies this way, it allows us to continue production of this key item, ensuring high quality, and lower costs for our customers.
Purchase here
The thermo body is a component which will sometimes need replacing during restoration work. The union for the outlet pipe has a very fine thread that is easily damaged, especially with any build of corrosion. The thread used isn’t a common thread size making it very difficult to be able to retap, so having new bodies available is essential.
As a complete unit, the thermostatic choke was predominantly used on Jaguar saloons with either H or HD type carburetters, but was also used on a few other applications. The unit is designed to provide automatically differing degrees of mixture enrichment at:
- Starting
- Idling and light cruising conditions
- Full throttle conditions
The unit is controlled either by a thermostatic switch housed in the cylinder head coolant jacket, set to bring the apparatus into operation below 35°C (95°F) or alternatively with a manually operated switch on the dash which is usually provided with a warning light.
The device comes into action by energizing the solenoid. The iron core inside raises carrying with it the ball jointed disc valve against the load of a conical spring. This opens the aperture between the valve and the seating in the body.
Air in is then drawn through the intake passage and mixed with fuel as it passes the jet. The mixture then passes upwards past the shank of the needle, through a passage then out through the aperture between the valve and the seating. This will provide the necessary rich mixture for cold starting.
For more information on the thermostatic choke operation, including tuning and adjustment you can see our full technical article online here.
