Can't fix fast idle
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New User
Joined: Jan 2007
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Can't fix fast idle
OK, I replaced the 1bbl on my '66 F100. Everything looks great, but I can't get the idle down to a normal level. It runs at about 1500 RPM. I can take my foot and pull the gas pedal up to get it to an almost OK level, but it always goes back to 1500 or so after I use the accelerator again. Also, the choke is pretty much not needed any more, I guess because the idle is so fast.
Anyway, I have adjusted the carb every way I know how to no avail.
Any ideas on how to take care of this? What am I missing?
Anyway, I have adjusted the carb every way I know how to no avail.
Any ideas on how to take care of this? What am I missing?
Cargo Master
Joined: Jul 2006
Posts: 3,014
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From: Concord, CA
You can pull up on the gas pedal and the idle speed will drop to near normal? After you remove your foot it works its way back up to 1500 rpm? Sounds more like you have a problem with your accelerator linkage somwhere between the pedal and the throttle lever on the carb. Any places where it is hanging up or binding and not returning to full relaxed position? What happens when you disconnect the linkage from all contact with the throttle lever? If the lever is all the way forward, with normal idle, then check the linkage components. If forward and the idle is high what is the fast idle cam doing? I am more familiar with a 2100, 4100 and 4300 in my mind.
Junior User
Joined: Nov 2006
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I had this same problem a while back. In my case, it was a simple problem that you may already have ruled out: the throttle return spring was attached improperly. I had removed the spring and replaced it, placing one end in a hole closer to the carb, thus reducing the amount of tension in the spring. The vibration from the engine literally bounced the throttle open, causing a very fast idle at times. If you can reduce the rpm by holding the throttle closed at idle, you might be able to solve the problem by readjusting or replacing the spring.
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Thanks guys. I tried the return spring as the cause, even putting a very tight spring on it to try and fix the problem. No dice. The linkage, if anything, seems too loose. It seems as if it could be tightened somehow, that might fix it. Honestly, I don't know what the fast idle cam is, so it's hard to tell you what's going on there.
Thanks again for the feedback.
Thanks again for the feedback.
Postmaster
Joined: Nov 2001
Posts: 3,351
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From: Escondido, CA
The fast idle cam is located on the same side as the choke linkages. The choke is the plate that closes when the engine is cold to help increase the air to fuel ratio until it warms up a bit. Look closely at the side of the carb and you will see a little stepped swing arm,fast idle cam, that moves freely with the choke plate held completely open. If it doesn't move open the throttle just a tad until it to moves. There should be a little adjustment screw/bolt that contacts the fast idle cam. Adjust this as needed to obtain a 900-1200 rpm idle when cold. As the engine warms up less cam is needed and the RPM should drop down in little increments until the choke is full open. It may take a few tries to get it right.
The link takes you to a autoparts store website that has pictures. Scroll down until you see your carb or one similar to it. It may or may not help but it gives you something to go on.
http://www.autozone.com/servlet/UiBr...3d800acdd5.jsp
The link takes you to a autoparts store website that has pictures. Scroll down until you see your carb or one similar to it. It may or may not help but it gives you something to go on.
http://www.autozone.com/servlet/UiBr...3d800acdd5.jsp
Last edited by airharley; Mar 4, 2007 at 11:04 AM. Reason: link needed
Lead Driver
Joined: Aug 2003
Posts: 6,305
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From: Boulder Creek, Ca
First and formost, Welcome to FTE: 
Sorry, not familiar w/ 1 brl. carb., may want to check needle valve setting. Close needle valve, not too tight, and back off about 1 1/2 turns, fine tune once you set close to a desired idle. Had simular problem after rebuilding carb., thought must have messed up rebuilding carb only to find I had connected the vacuum advance hose to the wrong inlet fitting on the carb. Wonder if another possiblility could be the timing, want to make sure when setting the timing that the vacuum to carb, and distributor are both plugged. Anyhow, none of the suggestions mentioned may apply but food for thought.
dave
Sorry, not familiar w/ 1 brl. carb., may want to check needle valve setting. Close needle valve, not too tight, and back off about 1 1/2 turns, fine tune once you set close to a desired idle. Had simular problem after rebuilding carb., thought must have messed up rebuilding carb only to find I had connected the vacuum advance hose to the wrong inlet fitting on the carb. Wonder if another possiblility could be the timing, want to make sure when setting the timing that the vacuum to carb, and distributor are both plugged. Anyhow, none of the suggestions mentioned may apply but food for thought. dave
Last edited by daveengelson; Mar 4, 2007 at 07:12 PM.
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OK, yes I had tried adjusting that to no avail. Just didn't know what it was called. I looked at it again today, and the bottom of the cam was on the manifold, keeping it from being adjusted right. Once I took some pliers and got that piece away from the manifold, it worked fine.
Thanks for pointing me in the right direction!
Thanks for pointing me in the right direction!
