my truck is a 78 f-250 4x4 with a 400 C-6
my automatic choke has been acting up thinling of going manual but thought id check on here see if anybody could help. i set evrything by the ford procedure. worked great for a few days then the choke woudlnt open up all the way and could get the idle to drop down. changed the choke thermostat reset everything. worked good for few a days. back to the same. any ideas???

 

What is the voltage input to the thermostatic (choke) spring?

 

i have only checked it with the truck running and it was 14.7 volts

 

Does it have the motorcraft two-barrel? If so the electric part only assists in opening the choke. The main source of making the choke open is the hot stove pipe coming from the exhaust manifold or intake manifold.

 

It should be about 9 volts. It should be the wire comming off the back of the alternator.
Other wise it will be too fast.

 

yep its a motorcraft. can the hot stove pipe go bad? it is hooked up. what else is there to check for? 9 volts? from the alternator? is there suppose to be a resistor in th wire to step the voltage down?

 

The wire from the alternator is from the stator, it is AC so will not read a full 14v on a DC scale of your voltmeter. Check the ground side of the choke coil. That is the tab on the coil, it grounds thru the strap that secures it to the carb.
To check the heat stove, check for vaccum at the port at the back of the airhorn of the carb. Clean air is drawn in at this point, passes thru the heat stove and into the choke. Any leaks the choke will not fully come off..... Don

 

Also what setting do you have the choke on? This seems crazy but.... if you set the choke to rich side in cold weather it will take too long to unwind because in the cold it is already wound tight and rich makes it even tighter. In cold it is better to move towards lean so it can pull off when it warms up, which takes a while. In warm weather... if you set towards lean the spring is starting at a unwound position and lean will pull it off way to fast. So a bit rich will slow it down as a freashly started engine is still a cold engine.
Hope that made sense.

 

rechecked the voltage to the it is 14.7 volts on the dc scale, gonna have to check where that wire is coming from, the stove pipe is inplace and hooked up to the tube on the airhorn. the thermostat is set on the index setting i think that whats its called its between rich 1 and lean 1. and yes Kennewick that does make sense.

 

The correct wire from the alternator on mine comes right off the back of the alternator and is covered with a cloth insulator to get it up to the top of the intake. On mine I removed the hot air tube and when I had the manifolds shaved I took off the little door that is the plenum for that tube. If you were to look at that plenum is greatly restricts the exhaust flow on #4. So I just augered the metal out and opened the mainfold up. then had a friend weld the door and tube hole shut. Huge increase in flow. Then I purchased the electronic choke from LMC which has worked great. Hooked up to the 9.5 volt wire it takes around 5 min for it to fully open in real cold weather set at the 0 position. Then I added the later model warm air controls and a thermostatic air cleaner with a cold air intake that auto maintains air temp to the carb. I get great MPG, starts every time with just a single pump to set the choke and on the highway the intake is a very noticeable increase in performance. take some time and fully understand the choke system you have and with a bit of "messen" around you will get it down tight. Some of that stuff everybody yanks off was well engineered. Good luck. Keep asking questions.

PS don't confuse the 0 mark on the choke spring housing with the index mark on the fast idle cam area. Fast idle set screw is on the back passenger side of the carb. Installed it is hard to see the v mark. Here is some good info. Specificly check out step 6. http://www.hurtle.com/cars/mustang/fixes/carb/
Here is a good write up on thermostatic air cleaners. http://www.scribd.com/doc/22301449/A...r-Thermostatic

 

The vacuum supply can get plugged off internally of the carb. or the pipe can litterally seperate from the manifold,therfore suck cold air instead of hot filtered air. Or a previous owner didnt know what they were doing and disconnected it thinking it was a smog device... Otherwise, not usually a problem.

The choke uses the altenator's stator connection. If you check it with a DC meter it will read aproximately 7 volts DC, if working correctly.

If it's reading 14+ volts DC the choke is hooked up to the battery somehow, or the altenator is defective on the stator circut.

Make sure it's not 14 volts AC that you are reading. That would be about normal

That extra voltage will heat up the spring inside the choke cap too much and warp it and eventually destroy it. Most likely why it wont stay adjusted properly.

 

More useful reading:

https://www.ford-trucks.com/forums/8...ml#post6939116

 

Awsome post

 

thanks for the help guys. will let you know how it goes