Carb Question
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Cross-Country
Joined: Sep 2008
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Carb Question
Ok, here's what I've got; 81 F100 with a 300 6cyl. Low miles everythings in good shape.
Here's my problem, When I start the truck in the morning and get it warmed up it runs fine. But, after I've driven it a few miles, shut it down and then go to restart the motor, it's really hard to start unless I've got the pedal mashed to the floor, and then it just barely starts. Once it's running, it will idle rough until it finally pick's up, and then will run just fine. It will also belch out some black smoke when it's trying to idle up to normal.
I know it sounds like it's flooded, but when I go to start the truck, (after it's warmed up) I don't punch the pedal. But, after a few cranks, unless I mash the pedal to the floor, it simply will not start.
This truck does not burn oil, so I assume all the black smoke is from burning off the excess fuel in the carb?
I've got the choke adjusted where flap will close at cold start-up and gradually open while it's warming up.
Is this a simple choke adjustment that I'm not getting right?
Here's my problem, When I start the truck in the morning and get it warmed up it runs fine. But, after I've driven it a few miles, shut it down and then go to restart the motor, it's really hard to start unless I've got the pedal mashed to the floor, and then it just barely starts. Once it's running, it will idle rough until it finally pick's up, and then will run just fine. It will also belch out some black smoke when it's trying to idle up to normal.
I know it sounds like it's flooded, but when I go to start the truck, (after it's warmed up) I don't punch the pedal. But, after a few cranks, unless I mash the pedal to the floor, it simply will not start.
This truck does not burn oil, so I assume all the black smoke is from burning off the excess fuel in the carb?
I've got the choke adjusted where flap will close at cold start-up and gradually open while it's warming up.
Is this a simple choke adjustment that I'm not getting right?
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From: Virginia
It could be. When you go back out to start it later on(when you have all the trouble) before you do anything open the hood and take the aircleaner off. Push the throttle open a little bit with your hand. Is the choke door straight up and wide open or does it close some? If it closes, adjust the round black piece on the side of the carb till the choke door is open. Then try it. It probably won't start too well after you have adjusted it, since each time you move the throttle you are squirting gas in the carb.
After all this, you might find it now won't start when it's cold. If that happens, then I would look at the metal line that goes up to the choke, and all the other parts of the choke. It all has to be there and hooked up or it won't work right.
After all this, you might find it now won't start when it's cold. If that happens, then I would look at the metal line that goes up to the choke, and all the other parts of the choke. It all has to be there and hooked up or it won't work right.
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Cross-Country
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Ok, when I cold started it this morning, the choke door was closed. Engine started right up, but idled rough and almost stalled until I pushed the door almost wide open.
I cranked the black adjustment dial to the left (facing the engine from the front) and it never opened the flap on it's own. Once the motor finally warmed up a bit, the choke door opened up about halfway and that's where it stayed. Motor seem to idle ok, but I'm sure I'll have the same problem later where it won't start after it's been run for a while..?
I cranked the black adjustment dial to the left (facing the engine from the front) and it never opened the flap on it's own. Once the motor finally warmed up a bit, the choke door opened up about halfway and that's where it stayed. Motor seem to idle ok, but I'm sure I'll have the same problem later where it won't start after it's been run for a while..?
Lead Driver
Joined: Jul 2009
Posts: 6,477
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From: Sheffield, AL
The choke plate must be able to open fully in order to run correctly. I've attached a link which might give you some food for thought.
https://www.ford-trucks.com/forums/1...ent-101-a.html
https://www.ford-trucks.com/forums/1...ent-101-a.html
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From: Virginia
You need to hold the throttle open while adjusting the black round piece. You are affecting the idle speed as well as moving the choke door when you are adjusting this thing, and it does not have enough power to move the throttle, so you have to hold it open. The best way is with the engine off, get someone to hold the gas pedal down in the cab while you adjust it.
That's also why before you start it in the morning, you need to kick the gas pedal at least once before starting it to "set the choke". That is to release the pressure of the throttle off the choke so it can shut. That's also why if you leave it running in the morning and go back in the house to let it warm up, if leave it running very long it it will be running at a very high rpm and you need to "kick" the gas pedal to idle it down. It just doesn't have enough power in the choke spring to do it itself with the throttle pressing on it.
That's also why before you start it in the morning, you need to kick the gas pedal at least once before starting it to "set the choke". That is to release the pressure of the throttle off the choke so it can shut. That's also why if you leave it running in the morning and go back in the house to let it warm up, if leave it running very long it it will be running at a very high rpm and you need to "kick" the gas pedal to idle it down. It just doesn't have enough power in the choke spring to do it itself with the throttle pressing on it.
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Cross-Country
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Ok, that explains why the choke flap did not move as I was adjusting the black dial on the back (while the engine was running). I was adjusting the choke flap and then the idle separately, so now I've got to get that back to where I started.
When I punch the pedal in the morning, the flap closes to within a 1/8 or less and the motor starts just fine, the problem is the flap does not open once the motor has started. So, this is where I need to adjust the choke flap to open after the motor has started and then warmed up.
What is the wire for? electrical assist to the choke?
Thanks a lot for the help! I'm learning, albeit slowly.....
When I punch the pedal in the morning, the flap closes to within a 1/8 or less and the motor starts just fine, the problem is the flap does not open once the motor has started. So, this is where I need to adjust the choke flap to open after the motor has started and then warmed up.
What is the wire for? electrical assist to the choke?
Thanks a lot for the help! I'm learning, albeit slowly.....
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Lead Driver
Joined: Jul 2009
Posts: 6,477
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From: Sheffield, AL
The wire is to provide electricity to the small choke heating element located in the choke housing. It runs to the alternator [s stator?] and provides current only when the engine is running. If measured with a volt meter, it should be approximately 7 volts. The heater works in conjunction with the hot air provided by the exhaust manifold through the insulated metal tube.
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From: Virginia
The electric wire doesn't work all the time from what I understand, it assists the choke in opening only at certain temperatures. The hot air line(the metal tube) is the most important piece in this setup. If it's working right, you can put your hand on it and it will get warm as the engine runs.
Also, the first start in the morning, when you kick the throttle for the first time, the choke should shut completely with no gap. When the truck starts it builds vacuum, and there should be a round metal piece somewhere on the carb with a vacuum line running to it. It will have a lever coming out of it, and after the truck starts, this lever will crack the choke open. This is called the "choke qualifier" or "choke pull-off". These do go bad, and can get out of adjustment.
If you find what I am talking about, you can take the lever coming out of the vacuum thing and pull it back, and you will see what it does. Usually you bend this lever for the adjustment, but I would not do that unless you have to.
Also, the first start in the morning, when you kick the throttle for the first time, the choke should shut completely with no gap. When the truck starts it builds vacuum, and there should be a round metal piece somewhere on the carb with a vacuum line running to it. It will have a lever coming out of it, and after the truck starts, this lever will crack the choke open. This is called the "choke qualifier" or "choke pull-off". These do go bad, and can get out of adjustment.
If you find what I am talking about, you can take the lever coming out of the vacuum thing and pull it back, and you will see what it does. Usually you bend this lever for the adjustment, but I would not do that unless you have to.
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From: Virginia
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