I just got a 1984 F-250 4x4, 351w, 2bbl carb with auto trans. I have been tuning it up and there is a unit near the carb that I can't figure out it's function? It looks like some type of vacuum divice for the throttle control. It is mounted on the drivers side beside the carb, it is a round cylinder about an inch in diamater and 2 inches long. It has a rod that comes out and touches the throttle stop position. If I hold the throttle open the rod will pull out manualy with my fingers. It seems to have a vacuum line and an electrical connection also. It is adjustable by a long skrew and spring on the bottom. The divice doesn't seem to be working, i've had the truck running in all conditions in the last two weeks. Can someone tell me what this is?

Thanks,

Randy

 

Sounds like a "throttle kicker". These served two purposes (that I know of).
One was when the air conditioning was turned on the idle was raised. AC puts an extra load on an engine and could make the engine idle down enough to actually die. I have actually had this happen with a disconnected/broken throttle kicker. Simple way around it is to just up the idle adjustment to where the RPM's at idle are always a bit to high except when the AC is on. If you don't have AC, or AC that works, you don't really care about the kicker.
The second purpose is as an anti-dieseling device. With an engine that has a very lean idle from the factory (for lower emissions) and that also runs at a fairly high temperature (also for emissions) it's pretty easy to get engine run-on or "dieseling" after the ignition has been shut off. In this case the kicker is energized whenever the engine is running and controls the idle speed. If you wanted to adjust the idle you would adjust a spring loaded screw thingy on the side of the kicker that would move the entire kicker back and forth. As opposed to just turning the more usual idle screw. When power was shut off (key turned off) the kicker would retract completely. This would allow the throttle plates to close completely, shutting off all air to the engine so it couldn't diesel. IIRC, such setups also had a regular idle screw that could be used to override a dead kicker if need be.
There may be others, these are the only two I know much about. I don't know if the two functions were actually combined in one unit, but I don't see why not. I don't recall a vacuum line to these things, just wires. So the thing could indeed be something else.

 

Actually it looks similar to a vacuum advance on the distributer only smaller, vacuum line and electrical line from it. And yes it does adjust the throttle when I turn the adjustment screw.