Re: First Water Choke

[rvpapasso]

There are two parts to the choke, the vacuum pull off and the thermostatic spring. The vacuum pull off closes the choke plate in the absence of intake manifold vacuum. When vacuum is present the vacuum pull off releases the choke plate. When the choke plate is released the amount the choke plate is open is dependent on the thermostatic spring.

Given the above when the engine is not running the vacuum pull off forces the choke plate closed regardless of the position of the thermal spring. However any vacuum in the intake manifold during cranking will tickle the vacuum pull off slightly releasing the choke plate and then forcing it shut between vacuum pulsations. This is where the flutter comes from. Once the engine is running and there is steadier vacuum in the intake manifold the vacuum pull off completely releases the choke plate to be controlled by the thermostatic spring.

The amount of choke is then dependent on the thermostatic spring based on the temperature of the water passing through it. When at proper operating temperature the thermostatic spring will hold the choke full open. This part of the choke is adjustable to be leaner or rich during warm up. If adjusted properly the engine will run smooth from cold to operating temperature. Once the engine is stopped the vacuum pull will close the choke fully regardless of the temperature.

Carter had a similar choke setup for cars that was called a "climatic control". It also utilized a vacuum pull off and thermostatic spring.