Hey Everyone;

I need some help. I've got a 84 f-150 with a 4.9l inline 6, 1bbl carb.
Has been running great until the weather turned cold. Here is what I have already repaired/replaced:
- Fuel Filter
- PCV
- Heat Riser Tubes
- Carb retaining bolts were tightened
- Distributor cap and button
- water remover in gas tank

The truck ran ok for a couple of days but it has returned to doing the same thing after raining: Starts fine, but then after warming it will run very rough, stalling after being stopped at a red light. I can restart it by pressing the gas pedal to the floor as if it were flooded. The gas mileage is pretty bad.

Here is what I've also noticed:
#1 - The carb has an electric choke but when the engine is warm, the choke is only open maybe a 1/4 way. I don't understand why the heat tubes are needed with an electric choke.
#2 - I can move the black cover on the choke just a little with my hand...is this normal?
#3 - Why did the problem return after it rained. I get the cold weather issue, but not the moisture.

I know it's alot to ask, but I would really appreciate any help you could offer.
This is by far the best site for problem solving!
Thanks for reading!

 

With the engine shut down pull back on the throttle a bit and check the action of the choke plate. Do this with a cold engine. As soon as you pull the throttle back the choke should leave the open position and snap into the cold start (shut) position.

With your finger move the choke plate through its entire travel distance. It should move freely with the exception of the resistance felt from a properly setup thermostatic spring. Even if everything checks out go ahead and lubricate the choke plate shaft where it rotates in the airhorn. This is all routine tune up maintenance but chokes seem to get neglected by many mechanics.

Now you can start the engine. The engine if everything else is O.K. should run on its own at a fast idle. When the engine reaches running temperature you should be able to tap the throttle and the engine will fall to normal idle and the choke plate should be wide open.

If you see anything much different then you may be able to adjust the thermostat. I'm not sure about your model, but many have 3 screws on the choke housing that you can loosen and turn the center to add or reduce spring tension. Which ever is necessary.

If the choke is free, is getting voltage (if electric), and is not reacting then you need to replace the spring.

One thing is FOR SURE! That thing only being 1/4 open when warm is definitly wrong. I hope some of this info leads you to why it is shut. Also look at possible rods or linkages on the carb being bent causing hangup.

You may want to change your plugs if this vehicle has been like this for a while.

 

Check and make sure the air intake preheating works properly, especially in a straight six engine it makes a night & day difference. If the preheat is faulty, you can seriously freeze your carb and symptoms sound quite a lot like that.

 

I'll give all your suggestions a try...Thanks!