I have an 84' F250 with a 351W and a 2150 with electrically assisted choke. The truck has been sitting for a while, and I'm having a problem where when you press on the gas before a cold start, the pulldown is not closing the choke plate. If you wiggle the pulldown mechanism a bit and then press the gas it closes normally and the truck fires up fine.

Once started, the step-down works fine to step down from cold to the middle position and then to warm idle. There is something in the linkage that is just not quite catching the pull down mechanism but I can't figure out what it is. It used to work fine but I'm afraid that with it sitting around something isn't quite as willing to move as it once was.

I think I can figure out how it works off the truck, but I don't want to pull it off unless I have to.

Thanks,

Bryan

 

The pull-down is supposed to open the choke, not close it. When you hit the gas in the morning to cold-start, the tension of the choke spring should snap the choke completely shut. If not, there is binding in the fast idle linkage, the choke is lean, or the choke is worn.

Once you start cranking the engine, engine vacuum pulls the pull-down diaphragm which opens the choke slightly to get the engine to fire. Once running, engine vacuum makes the pull-down hold the choke open until the choke starts warming up and takes over opening the choke the rest of the way.

 

Okay, my terminology is off here. Thanks for the clarification. there are so many little parts in there I can't remember all the names!

The problem is that when I step on the gas, the choke plate does not snap shut unless I fiddle with the linkage a bit. The spring is fine, it's obviously binding up somewhere. I'll probably look at the fast idle linkage first.

What do you mean by the "choke is lean"? I've never heard that term before.

Thanks,

Bryan

 

Lean means that the choke isn't closed enough. You can loosen the three screws holding the choke cap on, and rotate it. Turning it toward the back of the truck makes it rich, and turning it towards the front makes it lean. There is a mark on the top of the cap that will line up with a mark on the choke housing (the metal part attached to the carburetor). On the choke housing, there is a middle mark, 3 lean marks and 3 rich marks. Starting from the front and going back, they are ordered 3-lean, 2-lean, 1-lean, middle, 1-rich, 2-rich, 3-rich. The valve cover sticker will say which mark to set the choke on...although many times it's more of a trial-and-error thing.

The richer the choke is, the tighter the spring will be, and the longer it will take to heat up enough so that the plate begins to open. Hence, the longer you'll be running rich while warming up. If your choke spring is really worn out, which is common for really old caps, the choke will behave as if it is set lean even though you have it set to be rich.