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84 2.0 carbed fuel system opinion


neinnein_nein

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But just to double-check that I’m not trippin here—turning the black circular thermostat counterclockwise on the carb will make it so that the choke is initially more closed, which makes the mixture richer (less cold air, therefore more fuel), which makes it easier for the engine to turn over.
sorry this sounds so dumb but there’s still something in my head that resists understanding carbs. I watched videos with 3D graphics etc, I still don’t fully get it. I mean it’s really cool that it’s just a bunch of screws and springs and weird chambers squirting gas into each other, it’s a pretty crazy invention.
 


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Just to be safe put a mark on the carb body to line up with a mark on the choke cover. There should be some marks already there but maybe only on the factory adjustable carbs. You can move the choke cover clockwise and watch the linkages open up the choke. Moving it counterclockwise will put more spring pressure onto the choke mechanism making the engine need to be warmer before the choke starts to open.
There are other adjustments that can be made but its been to many years since I've worked on carbs.
IIRC when the engine is cold and you blip the throttle (not running) the choke should completely close off the air horn. Once the engine is started there should be about an 1/16" to 1/8" opening at the bottom of the butterfly valve, and that should slowly open up as the engine warms up. There are linkages and procedures to adjust the linkages to obtain these setups but I don't know anymore.
 

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Another point I forgot. There will be a small pipe that comes from the intake manifold too somewhere very close to the choke mechanism. That carries warm air to the internal choke spring and relaxes tension so that the choke plate can open more with more heat. Those have a habit of corroding and breaking loose. If that happens then the choke won't work.
I should mention all my knowledge of carbs is on 60's and 70's v-8's. So there will be some differences between what I have worked on and your setup.
 

rusty ol ranger

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My 83 F150 had screws to adjust the choke...but it was non feedback. I dont know alot about the feedback setups.

Automatic chokes are amazing when they work.

Ron, ive found those little 1 barrel carbs will not start when cold without a choke. My 2150 2bbls will but they arnt happy about it. Thats why i mentioned the choke. That little YFA 1 bbl on my 300 i had if it got below 35 or so once the choke quit it would not start unless i ethered it. Even then it was a pain to keep running.
 

19Walt93

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The feedback solenoid on the side of the carb is worth checking, too. We had a ton of trouble with those back then. With the key on and the engine not running touch the solenoid and you should feel it clicking on and off. If it doesn't click you may be able to clean it with throttle body cleaner, unplug the solenoid and remove it, turn it upside down and flush cleaner through the ports. Prop it up in and upside down position and let it dry for a 1/2 hour or so, reinstall it and try it again. Ford never approved cleaning them but it might save you trying to find a replacement. When those solenoids started failing in 83 the dealer cost was about $98, after they paid for a bunch of them on warranty claims the cost dropped to $12. At the time Ford allowed dealers to mark up warranty parts 30%, 30% of $12 is a lot less than 30% of $98.
 

neinnein_nein

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The feedback solenoid on the side of the carb is worth checking, too. We had a ton of trouble with those back then. With the key on and the engine not running touch the solenoid and you should feel it clicking on and off. If it doesn't click you may be able to clean it with throttle body cleaner, unplug the solenoid and remove it, turn it upside down and flush cleaner through the ports. Prop it up in and upside down position and let it dry for a 1/2 hour or so, reinstall it and try it again. Ford never approved cleaning them but it might save you trying to find a replacement. When those solenoids started failing in 83 the dealer cost was about $98, after they paid for a bunch of them on warranty claims the cost dropped to $12. At the time Ford allowed dealers to mark up warranty parts 30%, 30% of $12 is a lot less than 30% of $98.
This thing right? Mines a new one, CDÂme with a reman carb i bought so I think it’ll work..
 

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RonD

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Whats carbs do

Gasoline has best burn when a cylinder has a 14.7:1 ratio of air:gasoline, this is a WEIGHT RATIO
14.7 POUNDS of air to 1 POUND of gasoline
14.7 grams of air to 1 gram of gasoline

The air opening size on the top of the carb is known, so the flow of air thru this opening can be calculated, the Jet sizes used are setup to meter gasoline flow to this 14.7:1` ratio based on the air flow thru that size opening

As the air passes by the Jets it SUCKS gasoline out of them, its not a very accurate system but works fairly well
Problem with Carbs was that the WEIGHT of the air varys by temp(hot air rises, because it LIGHTER), and altitude, air is thinner/lighter at say 4,000ft elevation than at sea level

The displacement of the engine is also known, a 2 liter engine can suck in 2 liters of air, every 2 RPM, at wide open throttle(WOT), so its just number crunching to know how much air will be sucked in at say 2,000RPM
A 3.0l engine pulls in 3 liters of air, 5.0l engine 5 liters of air, ect.................

So the carb's air opening is setup for engine displacement at WOT, and then the Jets are setup for that air flow
Too small an opening and you can't get full power, full air flow
Too large an opening and you loose SUCTION, so lose power

There is a float bowl to feed the Jets and also feed the Accelerator Pump, this pump squirts gasoline into the engine anytime you press down on the gas pedal, this makes for a Richer mix because of the instant increase in air flow with throttle opening quickly, without this there would be a hesitation as the Jets don't instantly react to the increased air flow as suction drops a bit when throttle is opened

Now thats ABOVE the throttle plate

Below the throttle plate are the Idler Jets, needle jets
These much smaller jets are used to get the 14.7:1 ratio at low RPMs, the MAIN Jets are too big to fine tune the idle
Generally the idler jets are tuned Rich, to prevent overheating at idle, and also to keep Cats nice and hot at lower RPMs


Why a Choke
Liquid gasoline can't be ignited by a spark, yes the movie guys take liberties with that one, lol
Only gasoline VAPOR can be ignited by a spark.
You need 30% gasoline vapor in a cylinder to get a good ignition with a spark plug

Cold gasoline has less vapor, if you can smell gasoline that's the Vapor you are smelling, and in cold weather it has almost no smell so no vapor

The Choke plate blocks air flow into carb but the engine cranking still pulls in the same amount of air
So what happens is MORE gasoline is sucked out of the Jets than normal
Even cold gasoline has some vapor, especially when sucked out of the jets
The choke is adjust to get at least that 30% vapor into the COLD cylinders so spark can ignite it
Once engine starts the cylinders warm up pretty fast, but the cold air being pulled in prevents much vaporization until the whole engine starts to get warm, so choke plate stays partially closed and opens bit by bit as engine warms up

This is why most vehicles had the air warmer pieces on the exhaust manifold, when cold air was sucked in from around the exhaust manifold to warm it up a bit to help engine warm up faster and run better cold
The Choke adjust also resets idle cam, so engine idles higher when cold, you set the automatic choke and high idle by pressing gas pedal to the floor ONE time before cranking
Engine should then start and idle high without any other input from driver, if things are working as they should

Manual choke needs to be set for start up and then adjusted as engine warms up



Fuel injected engines need the same thing, Rich fuel mix for at least 30% vapor and high idle on cold start
The computer does these things for the driver on cold start
Computer can also calculate air weight using air temp sensor and MAF or Barometer sensors
 
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19Walt93

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That's the solenoid, it's still worth checking. Ford released a vibration diag manual shortly after the Fairmont came out to address the problems caused by building a mid sized car that was lighter than a Pinto, since the older mechanics didn't want anything to do with chasing vibrations, I was "promoted" to chief vibration guy. The manual would often say to substitute a "known good" part and went on to say that means a part that you had verified was good, explaining that "new means new, new doesn't mean good". Good quality aftermarket reman is almost an oxymoron.
 

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hey Ron it’s a bit late but I wanted to say thanks a lot for the explanation. Still trying to wrap my mind about how to adjust carbs really but your writeup helped a lot. Trying to solve some carb-related problems related to the coming of winter and now at least it’s less esoteric because I finally understand that winter changes the weight of the air and throws the whole thing out of whack! That’s a start..
 

rusty ol ranger

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hey Ron it’s a bit late but I wanted to say thanks a lot for the explanation. Still trying to wrap my mind about how to adjust carbs really but your writeup helped a lot. Trying to solve some carb-related problems related to the coming of winter and now at least it’s less esoteric because I finally understand that winter changes the weight of the air and throws the whole thing out of whack! That’s a start..
Ill try to make it a lil simpler then ron...lol.

As air gets colder it gets denser. Meaning that, the actual volume of air getting sucked down the throat of a carb at 20* is considerably more then whats getting sucked in at 90*.

So if youre getting more air, you need more fuel.

A little trick i learned with carburators, is to adjust them when the ambient air temp is moderate for your area. Around here in michigan i usually adjust them when its around 50 or 60 outside.

It may run a lil rich when it gets 90-100*, and be a lil fussy wben it gets in the teens and 20s, but itll give you the best comprimise.
 

rusty ol ranger

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Id also like to add, make sure the engine is warned fully up when making any adjustments. Besides adjustmenta related to cold start (choke, fast idle, etc)
 

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The spec for fast idle is for setting it warm with the choke plate fully open, usually on the second step of the fast idle cam.
 

neinnein_nein

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There’s no marks on my choke anywhere, and the engine runs so smooth in both drive and P once it starts I knew it could only be the choke, but I was stupid and thought it was getting too much air (because it’s cold out etc). I would crank and pump the gas forever and it would only sometimes start with the pedal floored revving super high, and then it just clicked in my mind that the reason for this is that pressing the accelerator opens the choke. So it was too closed. Just nudged it in the direction of being naturally open a little and it’s already much more startable.

after attempts at starting I would also open the choke with my fingers to check on it and I would get this gas vapor coming out without being able to compute what the hell that meant. It just had zero air to burn that fuel.
Anyways uh life’s a journey I guess.
 

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And old thing I just remembered, instead of adjusting the choke for winter and summer we would put a wooden clothespin on the choke plate so it couldn't close all the way for summer then remove for winter
:)
 

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