What is this connection to my carb for?

[gbskunk2006]

I have an 86 GMC C1500 with a 4.3 Litre V6.  The previous owner did a real hack job with the wiring.  For example, he installed a toggle switch under the dash, with one wire grounded on the frame, and the other end leading to a green/white wire connected to some kind of plug-in at the top of my carb.  There is another pink wire connected to this plug-in as well which I'm assuming is the power source.

Hopefully, you can see the photo, but I'm just wondering what the purpose of this plug-in at the top of my carb is for? 

Thx in advance.

[dumbucket1]

Looks like the throttle position sensor but not real sure.

[VileZambonie]

Do you mean the electrical connection on the top of the air horn? That's the mixture control solenoid. You have a feedback carburetor.

[gbskunk2006]

Yes, that's exactly what I'm referring to, that electrical connection on the top of the air horn.

Next question.  Why would the previous owner basically have a on/off toggle switch for this?

Thx

[VileZambonie]

because I guess he felt like the computer wasn't doing a good enough job duty cycling it in milliseconds so maybe he figured if he flicked the toggle switch on and off 60 times in one second he could get better fuel economy 

Seriously - there is no reason to do that.

[gbskunk2006]

Well, since I'm not even sure if the switch was turned on/off in the past few years I owned the truck before starting my resto, I think I might just try going unplugged once I get it back on the road for a while.

Btw, the previous owner did do one hack that I do like.  He installed a kill switch in another hidden spot that I came accross accidentially.  That work's great as I definitely plan to keep it :-)

Thx again.

[VileZambonie]

hopefully it's a kill switch in a good spot. Don't put toggle switches on the primary side of ignition module or you may spike the module. If you plan on not running your feedback carb the way it should be you'd be better off with a non feedback carb.

[troop2]

The Grey plug on the top of the carb goes to a mixture enrichment solenoid. When the coolant is under 170 degrees the solenoid enriches the mixture for starting and cold operation. When the coolant warms above 170 degrees the solenoid energizes an leans the mixture out. It does not control the mixture constantly like a computor feedback  Carb with the blue plug. The problem with just unplugging the wire is the carb will run rich all the time.

JN

[cochese]

so what is this solenoid SUPPOSED to connected to?  how does it register the coolant temp. and energize the solenoid?

[VileZambonie]

Fuel flow through the carburetor idle/main circuit is controlled by MC solenoid controlled metering rods. The MC solenoid controls air/fuel mixtures by allowing more or less fuel to flow through the carburetor. The ECM controls MC solenoid operation by completing or breaking the solenoid ground circuit.
When the MC solenoid is energized (down position), fuel flow is reduced, providing leaner mixtures. When the solenoid circuit is open (up position), more fuel is allowed to flow, providing richer mixtures. The ECM cycles the MC solenoid ``on and off'' at a fixed rate of 10 times per second, but varies the amount of time that the solenoid is energized per cycle (dwell period) to control air/fuel mixture.