Truck is a 77 F100 with 300-6 C4 and a carter YFA single barrel. It has the electric choke.

Questions: The coil in the choke has an "U" shaped end. It seems it wants to keep the choke plate closed. Is the venturi effect from the air enough to open the choke plate?

When I try to set the choke with the throttle body lever, the pressure on the choke closes to where the fast idle cam screw does not rest in the step. It rests just above on the shoulder of the fast idle cam. Too much pressure or did I miss something?

Sorry if I don't make much sense. I'm trying to figure this thing out. I have read a lot of the other posts but it is just not sinking in.

 

Not familiar with auto choke on YFA. Most auto chokes have either an external vacuum chamber or a small vacuum piston in the choke housing to pull the choke plate open upon starting the engine. It is referred to as the "choke pull off". If it's the external, the little chamber could be bad and not pull the plate open. If internal piston, it could be gummy/sticky. There are adjustment specs.

It sounds like you need to install the choke cover properly. THIS IS GENERALLY SPEAKING. The black plastic cover with the coil spring and heat element may/should say Rich and Lean on it with graduation lines or the lines are on the choke housing. The cover or housing will have a single line or nitch at 12 o'clock position.

Try this. With the black cover removed, choke plate open, accelerator pedal held down so the fast idle cam will be free to move. Look at the open U of the coil spring, put the cover to the housing so the open part of the U is away from the link in the housing that the coil/U is going to go against. Now rotate the cover in the direction of the link. The U will engage the link and as you turn more it will start to close the choke plate. You keep turning until the black cover lines up with nitch or groove and it should dead center between Rich and Lean. The choke plate should be fully closed. Hold the cover there, push the choke plate open with a finger and let go, it should spring closed again. You have basically installed the choke cover properly. You need the spec for the position of the black cover. It could be right there at center line or it could be 1, 2or 3 lines the Rich side. There is gasket that goes in/on the cover/housing. It keeps all inside clean and may be more important if the Choke Pull Off is a piston in the choke housing.

All adjustments are usually done correctly at time of Mfg. or rebuild. Except adjusting the engine speed, idle smoothness and the fast idle cam speeds. you can get these specs procedure from manuals or maybe find online.

Hope this helps you, a little long but tried keep it simple as possible.

 

Thanks for the info.

Rebuilt the carb recently. I followed the instructions for the adjustments and watched the videos on the rebuild. Everything thing you mentioned was consistent with the rebuild and how the carb acts on the bench. I checked the adjustments again and it is according to the references from what I can tell. As soon as it stops snowing/raining and gets above freezing I'll see how it runs.

 

Glad to help a bit. Just curious, do you have an external choke pull off or internal piston type?

 

Internal piston.

 

Thanks, IF the internal pull off doesn't open the choke plate to your setting on startup, you might have chosen the wrong gasket between the throttle plate housing and the main body. It needs an immediate vacuum to the little piston. Be sure the piston is free moving.
Will look forward to how you make out.