Carb problem
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Senior User
Joined: Jun 2007
Posts: 394
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From: Springfield, Il
Carb problem
Hi, I have a Motorcraft 2100 carb. It has ran perfectly for the last 10 months that I have owned it. Suddenly the idle is very high at times. At traffic lights it is hard to hold back and will throw rocks when letting off of the brake. Idle is too high to put in nuetral. Sometimes it idles ok. I can back off the idle screw and it will still run fairly high. Just has me confused. Can any of you mechanics give me some suggestions on the cure for this. Or is a rebuild or different carb due. Thanks
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Senior User
Joined: Jun 2007
Posts: 394
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From: Springfield, Il
I decided to take the choke housing off and inspect. I found no piston. The rotating arm does not have an extension on it to hold the piston to begin with.
The truck had ran perfectly for months. The choke is a climatic choke and I have no idea if it should have the piston or not. Does anyone know.
My problem is that intermittently the idle is very high and sometimes it is fine. Burning thru a lot of fuel.
The truck had ran perfectly for months. The choke is a climatic choke and I have no idea if it should have the piston or not. Does anyone know.
My problem is that intermittently the idle is very high and sometimes it is fine. Burning thru a lot of fuel.
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
There is no piston on these carbs. The choke pulloff on a 2100 is mounted vertically on the air horn. It's situated outside of the choke housing completely; instead there is just a casting left over from earlier days.
It sounds like your fast idle linkage is binding. There is a fast idle cam that gets in front of the throttle stop on the passenger side of the carburetor when the choke is on. When it's engaged, the fast idle speed screw on the passenger side controls the idle speed, not the curb idle screw on the driver side. The fast idle cam is supposed to drop out once the choke is open. If it doesn't, there is a hex screw used to adjust the index of the cam. There's a small "V" notched on the cam to help align.
Take a look at the procedure in this post; you probably need to run through it: https://www.ford-trucks.com/forums/7...ml#post6422219
It sounds like your fast idle linkage is binding. There is a fast idle cam that gets in front of the throttle stop on the passenger side of the carburetor when the choke is on. When it's engaged, the fast idle speed screw on the passenger side controls the idle speed, not the curb idle screw on the driver side. The fast idle cam is supposed to drop out once the choke is open. If it doesn't, there is a hex screw used to adjust the index of the cam. There's a small "V" notched on the cam to help align.
Take a look at the procedure in this post; you probably need to run through it: https://www.ford-trucks.com/forums/7...ml#post6422219
Thread Starter
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Senior User
Joined: Jun 2007
Posts: 394
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From: Springfield, Il
I loosened the choke housing and turned it a touch to the rich side, also backed off the fast idle screw a touch and it seemed to have helped. Still had a little sticking though but nowhere near like it was. I have sprayed some carb cleaner on the choke mechanisms. Seems to be running better but not like it was.
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MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
To solve the problem completely, you'll need to run through the proper fast idle indexing procedure described in my other post. It's not so much the fast idle speed as it is the fast idle cam index that matters. Adjusting the choke setting or the fast idle speed does not change the fast idle cam's position relative to the choke (index). If you run through this procedure and still have issues, then something is likely bent.
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Thread Starter
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Senior User
Joined: Jun 2007
Posts: 394
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From: Springfield, Il
Sounds like good advice. I will do that. It is very hard to see the cam without climbing on top of the engine. Is this something that would be better done with the carb off and on the bench? Thanks
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
It's definitely easier to do with the carburetor on the bench, but in my opinion not worth the trouble of getting the carburetor off, which would mean draining the fuel, possibly changing the gasket, etc.
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