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1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks Discuss the Early Eighties Bullnose Ford Truck

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Old 07-12-2014, 12:21 AM
Widetrack455 Widetrack455 is offline
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12v choke conversion parts? 1980 F150 300" six Carter YFA

What parts actually fit and work on a 1980 300" 4.9L six 49 state version for conversion of the thermo/electric choke to straight 12v operation? I ask because some of the OE parts are missing from my truck to get the OE thermo heat plumbing to work. I'm thinking of converting to a straight 12v electric choke similar to what my old VW's use. I have extensively searched Google and this forum and found a few references but no actual part numbers. I thinking of using the Holley choke delay thermistor 45-267 to insure the choke has some degree of thermal sensitivity. Does anyone know which Holley 12v choke thermostat "part number" would fit the Carter YFA (in my case #7371s) and maybe work with the above listed Holley Electric Choke Delay? I'm looking at the Holley 45-258 Choke Cap Thermostat as a possible. Has anyone actually done this conversion? How did it work for you?

I want to do this conversion because of missing OE parts. If my parts weren't missing I would just use the stock setup. There is no use in my going to the local salvage yards looking for parts. EVERY Ford six (at least 75 vehicles) from 1960 to 1982 have already had the carburetors and exhaust manifolds removed. Long gone!!! No parts available. Carburetors are getting to be a rare commodity.

Looking to hear from someone who has actually done this conversion. Please keep in mind I live in Colorado. It gets cold, sometimes really cold and 100 degrees in the summer isn't uncommon. I need a choke that can deal with these temperature extremes. I know I can start drilling holes and install a manual choke. I don't want that.

Last edited by Widetrack455; 07-12-2014 at 12:37 AM. Reason: add part number
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Old 07-12-2014, 01:49 AM
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Can't say I have done such a conversion, or even contemplated it, but I just finished installing an Edelbrock carb with a full electric choke on my 83 351W F150. The Edelbrock is the same as the old Carter Competition carbs and I know the electric choke pieces are readily available. I think they may have a better chance of fitting your Carter YFA than Holley pieces would. Power it off the alternator stator like Ford originally did. Mine works fine.
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Old 07-12-2014, 01:50 PM
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Do you currently have an electric choke cap?

If so, just leave it as is. If you have a "hot air only" choke just add a stock electric cap.


TOMCO, INC. Part # 9104 $3.14

1984 FORD F-150 Carburetor Choke Thermostat / Heater

You also need to plug the hole for the hot air choke as it draws air into the carb.
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Old 07-12-2014, 06:34 PM
Widetrack455 Widetrack455 is offline
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My truck has the stock electric choke that connects to the alternator. What is missing is the heated air plumbing on both ends. From the exhaust manifold to the choke housing and the entire other side the allows the fresh supply.

In addition I'm also missing the hot air stove and flex hose for the air cleaner hot air supply. My vacuum motor is still there on the air cleaner but there are no vacuum hoses hooked up (I do know where they are supposed to be routed) and all the parts are there including the thermostatic vacuum switch. Just need to add the hoses but it won't do any good without the hot air stove.

My thoughts were to convert to a straight 12v choke since I'm missing so many parts by using the Holley Choke Delay (it's really just a thermistor, higher resistance when cold thus longer warm up cycle and low resistance when hot for a shorter warm up cycle) mentioned above and a new thermostatic choke designed for 12v dc instead of the Ford part that operates from the alternator. If I throw 12v straight at the stock Ford choke thermostat I'm afraid It burn it out quickly. The idea behind using the thermistor is it will monitor temperature and modulate the 12v choke thermostat. I was thinking of mounting the Holley Choke delay to one of the carburetor mount studs to facilitate carburetor temperature tracking.

The 12v chokes on my air cooled VW's work great. Just trying to simulate this on the Ford.

By the way the rest of the factory emissions equipment, smog pump and associated plumbing and cat are in place and working like they should. I need this stuff since I live in an emission control area.
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Old 07-12-2014, 06:40 PM
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I have read a couple posts on here from guys who have studied it more than me, that the Ford electric choke piece is a assist piece only, and does not even work in certain conditions. I forget exactly how it's supposed to work, but it may be the reason why I kept thinking mine were burnt out. It has a temp sensing switch inside the housing that doesn't even complete the circuit to the electric heating element until certain conditions are met. I can't remember if it has to be hot and it pulls the choke off quicker, or it has to be cold and helps pull the choke off quicker.

If you think about it for awhile, the hot air system is a very simple system that works well, and you could easily make the parts and lines out of universal fuel line or soft copper tubing from the hardware store. You could even just hook soft copper up to the housing, run it down and wrap it completely around the exhaust manifold a couple of times, and then run it back up to the port under the air cleaner. Just so it warms up the air in the copper tubing, it will work.
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Old 07-12-2014, 09:29 PM
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Franklin, thanks for the input. Guess I'll have to break new ground and order one of the 12v choke thermostats and couple it with the Holley choke delay device and see if I can get it to work like I want. My problem is I'm not sure the diameter of the various Holley choke thermostats are the same as the Carter YFA carburetor choke thermostat housing? If anyone knows please chime in.

Holley's website doesn't make it easy to determine which of their various choke thermostats (they have several) might be the best for my application or even if it will fit at all.

If I can't figure it all out I may try taking some soft copper and wrapping it around a hot part of the manifold like you suggested.

Somehow, using the Holley electrical parts seems like it might be a cleaner installation than using the hot air and copper tube approach? If I can get this to work I will completely block the vacuum source to the Carter YFA choke housing and remove that silly little easily gummed up piston assembly and rely on electric choke only. Just seems simpler and more straight forward than a hot air assisted electric choke that Ford designed for this application. Maybe my late 60's 12v VW's were a little ahead of Ford as far as choke activation and control is concerned?
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Old 07-12-2014, 11:31 PM
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The hot air system was crumbling when I got Dad's truck, so I hooked up the electric choke on the 2150. It worked fine, although I will admit that it wasn't as good as the hot air approach. But it worked well enough I didn't even think of making pieces to resurrect the hot air choke.
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Old 07-13-2014, 07:42 AM
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Quote:
Originally Posted by Widetrack455 View Post
remove that silly little easily gummed up piston assembly and rely on electric choke only. Just seems simpler and more straight forward than a hot air assisted electric choke that Ford designed for this application. Maybe my late 60's 12v VW's were a little ahead of Ford as far as choke activation and control is concerned?
Chokes are not easy to work on and get right the first time. They are a carefully orchestrated group of parts that all interact together so that when you start the engine under any conditions, you can just drive away.

That little piston you are talking about is the choke pull-off. I would keep it on there no matter what style choke you use. When the engine is cold, and you set the choke by pushing the gas pedal once, the choke door shuts completely. The engine will start right up under this condition, but will quickly stall out if the choke door is not cracked open a little bit. That's what that little piston does, vacuum reacts on it and it pulls back and cracks the choke open. Don't think you can carefully adjust the choke so it will keep running without it, been there done that. What's good for one temperature is no good for another.

The main problem with the thermistor system you want to use, is mounting it in the right location that will work. The exhaust manifold heats very quickly and cools off quickly relative to the rest of the engine. Of course you can't mount the thermistor on the exhaust manifold, you have to mount it to the block or the intake. There may be some delay with it's function in certain locations, you will have to experiment with it.
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Old 07-13-2014, 08:46 AM
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I have an all-electric choke and would LOVE to go back to the original... when the engine is totally warmed up, then shut off for a little while (20-30 minutes?) and then restarted, the electric choke insists on coming on again, that annoys the crap out of me. Apparently, it has gotten cold in that time and so it chokes the engine and raises the idle speed, hot-air-supplied factory variants don't do this as they are more accurately able to determine the engine's true temperature.

It sometimes amazes me what the engineers were able to accomplish using only temperature and vacuum and no computers to help.
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Old 07-13-2014, 09:08 AM
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I agree 100% with both Dave and Chris. The piston is very desirable to pull off the choke. Many carbs don't have that function and their chokes don't wrk as well. And, the hot-air choke does seem to handle warm restarts better than an electric choke. But parts to fix the hot-air choke aren't easily found. And, when you convert to an aftermarket carb, like I've done, the only option is an electric choke.
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Old 07-13-2014, 10:39 AM
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I may take the easy road too many times, but after I mess with these things for awhile, I usually go buy a manual conversion kit. If you set them up correctly they work good, the choke pull-off still works and the fast idle and the idle kick down works too. The last gas truck I had was carbed and it had a manual choke on it.
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Old 07-13-2014, 12:39 PM
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Ctubutis, interesting and very useful commentary on your electric choke. I hadn't given much consideration to choke re-application after a brief cool down. This is something I'll have to investigate before going further.

From my reading I understand that 12v electric chokes sometime heat up too fast and don't allow for a long enough warm up cycle unless there were some kind of control that insured current wasn't applied unless the engine was actually running but hadn't read about your issue with the electric choke.

My choke still has the choke pull off piston and linkage and stock Ford electric thermostat connected to the alternator. I haven't removed any of it yet.

This truck is new to me. I purchased it on the 4th of July 2014 and have been working through the bugs it had. 1st was improper oil level, there is another thread about that and this choke issue. Two days ago I rebuilt the YFA that had been attacked by a gorilla or fearless kid that didn't know what they were doing. The carb had a leaking accelerator pump and the wrong size check ball in the accelerator pump output circuit. Additionally the float level and float drop was set incorrectly for the application. As you can imagine it was using copious amounts of fuel, not responding to the idle air bypass screw, surging and dripping fuel down the throat of the carburetor from the accelerator port while idling. Additionally the carburetor had the wrong length screws and and springs for the curb and fast idle adjusters. For icing on the cake, the three long screws that hold the air horn onto the float chamber had been stripped and been replaced with longer screws and nuts. Happy to report it now runs like it should, curb idle at 600 rpm is very smooth and the engine reacts to changes in the idle air bypass screw like it should.

I don't have any of the fresh air supply plumbing for the choke. Currently the port on the air horn (the port that normally has the red silicone hose) has a plastic cap. Where is this hose supposed to terminate if I had one?
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Old 07-13-2014, 12:54 PM
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That's the fresh air intake. That's were the choke gets the filtered air.

Sounds like you know your way around carbs some. But I will run through how this system works.

They have a "on purpose" vacuum leak built into the carb that puts suction into the black round choke chamber. This chamber has a fitting on it somewhere for a line. I am not sure what the original line was, it might have been a steel hard line or some combination of hose and hard line. This hard line ran down and through the exhaust manifold. They usually had a special hole cast or drilled into the exhaust manifold, and the line from the choke ran through it. This is usually where it rusts out. After the line ran through this drilled exhaust area, it made a u-turn and ran back up and hooks into the port on the air horn you are talking about. That's where it opens up into the bottom of the air cleaner/air horn, and that's were this "vacuum leak" get's it's air supply from.

That's another little thing that I have run into on these trucks; They have a few of these controlled vacuum leaks for emissions stuff and the choke, and when you plug them off, that starts messing up your curb idle adjustment and that makes you turn the idle stop screw back some, and then that can mess up your idle mixture and it's adjustment.
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Old 07-13-2014, 01:10 PM
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Quote:
Originally Posted by Widetrack455 View Post
.

I don't have any of the fresh air supply plumbing for the choke. Currently the port on the air horn (the port that normally has the red silicone hose) has a plastic cap. Where is this hose supposed to terminate if I had one?

here is a photo that might help.
.

Click the image to open in full size.


Click the image to open in full size.
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Old 07-13-2014, 01:31 PM
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Franklin2, thanks for the info. Yes some controlled vacuum leaks are necessary otherwise it's just like holding your finger on the end of a straw filled with liquid. Without a controlled leak nothing changes.

Like most 300" sixes my choke hot air supply is rusted off. I believe I could get the dutchman out of the exhaust manifold and replace the hot air pipe with parts from the "Help" section from the parts store. My problem is I don't have a clue what the filtered air side is supposed to look like or where or how it enters the otherside of the exhaust manifold?

This ain't my first rodeo with Ford carburetors. I lived with lots of FE blocks and have a good deal of experience changing blown power valves caused from intake backfires. These YFA's have a similar problem but it is the accelerator pump that takes the abuse. Living at relative high altitude with a little less oxygen content and lower atmospheric pressure it isn't uncommon to advance ignition timing in an attempt to improve fuel mileage. Only problem is if you get a little too aggressive you run the risk of a power valve or accelerator pump damaging backfire! Usually one good pop back through the carb results in a blown power valve. The accelerator pumps on the YFA seem a little more forgiving but still rupture.
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