carb choke problems
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carb choke problems
hey, i have a 351w with a 4180 holley carb on it. the problem i am having is that the fast idle cam on the choke side does not seem to release and let the choke plate to open, those i am driving around with the choke on all the time, unless i pop the hood and manualy push the cam up. i don't know much about the electric choke on these carbs or how they work.
can any one help me fix this?
can any one help me fix this?
FTE Legend
Joined: Jul 2010
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From: Northeast, OK
The cam doesn't hold the choke on unless the linkage is messed up. The spring in the choke housing pushes both the choke and the fast idle cam off. At least, that's how it is supposed to work.
Let's start with the choke coil, which is inside the round, usually black, cap. That is a wound spring made of two metals that uncoils as it gets warmer. When the engine is cold the coil will bring the choke and the fast idle cam on. I don't remember how the 4180's choke is heated, but some chokes are heated by hot air pulled off of the intake manifold, or are supposed to be heated that way. Unfortunately the metal tubes that are supposed to carry the hot air disintegrate and the choke only gets cold air and won't pull off. Others have an electrical heater that assists the hot air, and still others only have the electrical heater.
So, you need to check your choke's coil to see if the hot air tube is still intact and if it is supposed to have an electrical connection but it has come off. I'm betting that something is wrong in that area which is why the choke won't come off.
Let's start with the choke coil, which is inside the round, usually black, cap. That is a wound spring made of two metals that uncoils as it gets warmer. When the engine is cold the coil will bring the choke and the fast idle cam on. I don't remember how the 4180's choke is heated, but some chokes are heated by hot air pulled off of the intake manifold, or are supposed to be heated that way. Unfortunately the metal tubes that are supposed to carry the hot air disintegrate and the choke only gets cold air and won't pull off. Others have an electrical heater that assists the hot air, and still others only have the electrical heater.
So, you need to check your choke's coil to see if the hot air tube is still intact and if it is supposed to have an electrical connection but it has come off. I'm betting that something is wrong in that area which is why the choke won't come off.
FTE Legend
Joined: Jul 2010
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From: Northeast, OK
I believe that choke takes 7 volts. Some of the others took 7, but I think my 4180 is marked 14. You should have that only when the key is on.
Last edited by Gary Lewis; Mar 12, 2012 at 09:51 AM. Reason: Correct major mistake
pedant
Joined: Jan 2008
Posts: 23,576
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From: EXTREME southwest CT
The single pin style Motorcraft choke element should get current from the Stator terminal of the alternator.
AC current reads as +/-7V DC on the meter.
You should have power only with the alternator turning. (engine running)
Check for a worn or binding linkage.
Some carb cleaner and a little light lubricant (MMO) might do wonders freeing things up.
If you can "push the cam up" and it stays where it should, makes me think the bi-metallic spring is doing what it should but doesn't have enough force to overcome friction.
AC current reads as +/-7V DC on the meter.
You should have power only with the alternator turning. (engine running)
Check for a worn or binding linkage.
Some carb cleaner and a little light lubricant (MMO) might do wonders freeing things up.
If you can "push the cam up" and it stays where it should, makes me think the bi-metallic spring is doing what it should but doesn't have enough force to overcome friction.
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thanks i'll check the voltage, but i think you are right and the linkage is getting stuck somewhere. this started a couple of months ago, so i few weeks ago i took the carb out and rebuilt it, cleaned it all up and i put some lubricant on the choke linkage, but it's still doing the same thing. could it be the plastic cam, or what do you think it could be. i'm pretty sure the choke kicks down when you touch the throttle after you started it.
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Joined: Jan 2011
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Fairfield, check to see if you are getting current to the choke, because without fire the choke will not come off reguardless of how many times you tap the gas pedal, I had the same problem and found that when my alarm was installed they cut the yellow and grey wires and connected them to the alarm, so when I removed the alarm I had the same problem that you are having, so I spliced the 2 wires back together and the choke started working again.
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FTE Legend
Joined: Jul 2010
Posts: 32,875
Likes: 48
From: Northeast, OK
The single pin style Motorcraft choke element should get current from the Stator terminal of the alternator.
AC current reads as +/-7V DC on the meter.
You should have power only with the alternator turning. (engine running)
Check for a worn or binding linkage.
Some carb cleaner and a little light lubricant (MMO) might do wonders freeing things up.
If you can "push the cam up" and it stays where it should, makes me think the bi-metallic spring is doing what it should but doesn't have enough force to overcome friction.
AC current reads as +/-7V DC on the meter.
You should have power only with the alternator turning. (engine running)
Check for a worn or binding linkage.
Some carb cleaner and a little light lubricant (MMO) might do wonders freeing things up.
If you can "push the cam up" and it stays where it should, makes me think the bi-metallic spring is doing what it should but doesn't have enough force to overcome friction.
I have my 4180 on the bench in front of me, and the choke mechanism has a coil spring wound tightly around the shaft coming out of the black choke housing and that closes the choke with authority. So, without the bimetallic spring inside the housing getting hot and overcoming the external spring the choke isn't going to come off.
As for linkage to bind, there is very little. The shaft coming out of the black choke housing is basically all that could bind, and that would have to be inside that housing. The fast idle cam rides freely on that shaft and is pushed by the external spring. So I guess it is possible for it to be stuck to the shaft. The only other linkage is the piece that goes to the choke valve, and it does pivot some in the ears it attaches to. Then there's the shaft of the choke valve. Pretty simple and few places to bind.
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pedant
Joined: Jan 2008
Posts: 23,576
Likes: 38
From: EXTREME southwest CT
I have my 4180 on the bench in front of me, and the choke mechanism has a coil spring wound tightly around the shaft coming out of the black choke housing and that closes the choke with authority. So, without the bimetallic spring inside the housing getting hot and overcoming the external spring the choke isn't going to come off.
As for linkage to bind, there is very little. The shaft coming out of the black choke housing is basically all that could bind, and that would have to be inside that housing. The fast idle cam rides freely on that shaft and is pushed by the external spring. So I guess it is possible for it to be stuck to the shaft. The only other linkage is the piece that goes to the choke valve, and it does pivot some in the ears it attaches to. Then there's the shaft of the choke valve. Pretty simple and few places to bind.
As for linkage to bind, there is very little. The shaft coming out of the black choke housing is basically all that could bind, and that would have to be inside that housing. The fast idle cam rides freely on that shaft and is pushed by the external spring. So I guess it is possible for it to be stuck to the shaft. The only other linkage is the piece that goes to the choke valve, and it does pivot some in the ears it attaches to. Then there's the shaft of the choke valve. Pretty simple and few places to bind.
You are quite right in that there is not much to bind.
I don't have a 4180 here to look at so I am going by memory of the number of times I have had one disassembled.
The coil spring on the shaft behind the choke mechanism could possibly become unhooked or lose it's tension.
The cam itself might not be free, as fairfield86 mentions he needs to push it up out of engagement.
But he does say " i'm pretty sure the choke kicks down when you touch the throttle after you started it."
So that leads me to think that his flap, rod, etc.. are free to operate.
FTE Legend
Joined: Jul 2010
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From: Northeast, OK
I'm changing my take on that spring. The more I play with the carb the more I'm convinced that the spring is only for the fast idle cam. Attached is a picture of the bottom of the spring, and it wraps around the fast idle cam on that end. With the carb on the bench that spring causes the cam to follow the choke itself - until the fast idle screw hits the cam, which causes the cam to stop until the throttle picks up and frees the cam. At that point it will swing to follow the choke, meaning that if the choke is on further the cam goes further and vice versa.
So, if that spring is bound up or corroded together it could cause problems. You can test that by holding the throttle open, maybe with a bungee cord, and moving the choke. Does the cam follow? Can you stop the cam and the choke still move, albeit with spring tension?
So, if that spring is bound up or corroded together it could cause problems. You can test that by holding the throttle open, maybe with a bungee cord, and moving the choke. Does the cam follow? Can you stop the cam and the choke still move, albeit with spring tension?
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just checked the voltage on the wire going to the choke. I turned the key to the run position, and i only had 0.149 volts on that wire holding my multimeter on the wire and the negative battery post.
tomorrow in the light i will trace the wire and see where it is going to, and if it is broken.
Also, would installing a manual choke fix this problem, and what do you guys like better.
tomorrow in the light i will trace the wire and see where it is going to, and if it is broken.
Also, would installing a manual choke fix this problem, and what do you guys like better.
FTE Legend
Joined: Jul 2010
Posts: 32,875
Likes: 48
From: Northeast, OK
just checked the voltage on the wire going to the choke. I turned the key to the run position, and i only had 0.149 volts on that wire holding my multimeter on the wire and the negative battery post.
tomorrow in the light i will trace the wire and see where it is going to, and if it is broken.
Also, would installing a manual choke fix this problem, and what do you guys like better.
tomorrow in the light i will trace the wire and see where it is going to, and if it is broken.
Also, would installing a manual choke fix this problem, and what do you guys like better.
Oh, duh! You said Run position, but not running. Fire the engine up for the test as the alternator has to be spinning. I'll bet you see ~7 volts on the DC scale.