Re: primer / injector system
Modern Mercs of which I have and am aware of, do not use a mechanical butterfly type choke any longer. Today it's called "fuel enrichment". On the remote control the key is rotated to the ON position and pushed in prior to starting....the next notch over.
When pushing the key in, voltage is fed to a switch in the engine that allows pressurized fuel (from the pressure the squeeze bulb generates) to flow into all carbs at the rear so that it basically goes into the intake manifold. This gives an enriched fuel charge to the intake manifold and assists in engine starting.
Years ago you had a mechanical lever that you pulled up and it had a butterfly over the air intake of each carb that, when the engine was rolled over in starting, it caused a very rich fuel mixture to enter the intake manifold.
Years later, with remote electronics and all, the activity was controlled with a solenoid operated from the control box. Still mechanical and old fashioned.
Then comes fuel enrichment which still uses a solenoid controlled by the ignition switch, but this time it injects fuel into the rear of the carb....aka intake manifold rather than controlling a rod with a series of butterflies on it.