New (rebuilt) Motorcraft 2100 - Crazy Fast Idle?
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Cross-Country
Joined: Sep 2015
Posts: 55
Likes: 1
From: Oregon
New (rebuilt) Motorcraft 2100 - Crazy Fast Idle?
So there's been a lot of first for me in the past week. I installed my first carburetor and, because I couldn't get the fuel filter canister off, I also installed my first mechanical fuel pump. For the most part this was all pretty straight forward as removing the old and replacing with new was a 1-to-1 operation.
All the same, I was absolutely shocked that after a few cranks on the starter the truck fired up and ran... but the idle speed was insane and I shut it down immediately.
So from those of you who've done this one or many times before, is this simply a matter of cranking down the idle speed screw or have I done something else wrong? The latter of which I'm completely willing to concede could have happened.
Carb is a Motorcraft 2100 on a 360 FE and I'm happy to fill in any other necessary details if needed.
Thanks very much in advance.
All the same, I was absolutely shocked that after a few cranks on the starter the truck fired up and ran... but the idle speed was insane and I shut it down immediately.
So from those of you who've done this one or many times before, is this simply a matter of cranking down the idle speed screw or have I done something else wrong? The latter of which I'm completely willing to concede could have happened.
Carb is a Motorcraft 2100 on a 360 FE and I'm happy to fill in any other necessary details if needed.
Thanks very much in advance.
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Make sure the throttle doesn't stick or isn't binding on something - like a thick gasket or something. Before starting the engine check that the throttle moves freely throughout its range and returns, and butterflies move to perfectly vertical no more no less when assistsnt floors pedal. Maybe back off on throttle adjustment a few turns and try again. Always keep a fire extinguisher ready and available in the truck, especially when working with a newly installed carburetor. Check that the fuel height in the bowl is correct once things settle down a bit.
Rabbit-Hole Researcher
Joined: Feb 2004
Posts: 466
Likes: 6
From: Middle of Ohio
A small amount of air gets pulled in through the 'fat leg' of the black choke housing. If it is missing the figure-8-like gasket, the hot-air tube, or the black-cap gasket, it could cause this.
When you get the RPMs down, water makes a good vacuum leak testing stream.
When you get the RPMs down, water makes a good vacuum leak testing stream.
Thread Starter
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Cross-Country
Joined: Sep 2015
Posts: 55
Likes: 1
From: Oregon
Make sure the throttle doesn't stick or isn't binding on something - like a thick gasket or something. Before starting the engine check that the throttle moves freely throughout its range and returns, and butterflies move to perfectly vertical no more no less when assistsnt floors pedal. Maybe back off on throttle adjustment a few turns and try again. Always keep a fire extinguisher ready and available in the truck, especially when working with a newly installed carburetor. Check that the fuel height in the bowl is correct once things settle down a bit.
I do have a fire extinguisher though, so thank you as that's excellent advice as well.
A small amount of air gets pulled in through the 'fat leg' of the black choke housing. If it is missing the figure-8-like gasket, the hot-air tube, or the black-cap gasket, it could cause this.
When you get the RPMs down, water makes a good vacuum leak testing stream.
When you get the RPMs down, water makes a good vacuum leak testing stream.
Lead Driver
Joined: Aug 2003
Posts: 7,592
Likes: 10
From: **** hole San Jose ca.
Hmm if the choke has been set by working the carb by hand the upper butterfly will close
almost shut.
This sets the Fast idea speed up to about 1800 rpm at startup.
All normal when a carb has been set up correctly. (edit)
Orich
almost shut.
This sets the Fast idea speed up to about 1800 rpm at startup.
All normal when a carb has been set up correctly. (edit)
Orich
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Here's some good links to steps that have proved useful:
http://www.junkyardgenius.com/holley/tune01.html
http://www.bob2000.com/carb.htm
http://www.junkyardgenius.com/holley/tune01.html
http://www.bob2000.com/carb.htm
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Cross-Country
Joined: Sep 2015
Posts: 55
Likes: 1
From: Oregon
I'll be getting back at it soon so I appreciate all this advice. Hopefully this is an easy fix as I don't think it's healthy for the engine to rev that high even briefly.
I'll report back on my progress.
I'll report back on my progress.
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Logistics Pro
Joined: Jan 2011
Posts: 4,762
Likes: 54
From: Antelope Valley ,CA
rebuilt carbs always need to be fine tuned to run correctly.
you will need to set the idle mixture screws , the choke fast idle , the idle speed.
you should also check dwell and timing to .
you tube videos will be a big help .
you will need to set the idle mixture screws , the choke fast idle , the idle speed.
you should also check dwell and timing to .
you tube videos will be a big help .
Thread Starter
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Cross-Country
Joined: Sep 2015
Posts: 55
Likes: 1
From: Oregon
I figured it out, and it's embarrassing, but I'll admit my mistakes.
I had not reconnected the throttle return spring. I don't know why that didn't occur to me since it's pretty clear something ought to hook up to the shiny mounting boss intended for that purpose.
Of course something else had to go wrong so now the truck won't start at all. All I get is the brake light lighting up on the dash, but nothing else. So yay, electrical problems. :|
I had not reconnected the throttle return spring. I don't know why that didn't occur to me since it's pretty clear something ought to hook up to the shiny mounting boss intended for that purpose.
Of course something else had to go wrong so now the truck won't start at all. All I get is the brake light lighting up on the dash, but nothing else. So yay, electrical problems. :|
Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
Likes: 783
From: Simi Valley, CA
So there's been a lot of first for me in the past week. I installed my first carburetor and, because I couldn't get the fuel filter canister off, I also installed my first mechanical fuel pump. For the most part this was all pretty straight forward as removing the old and replacing with new was a 1-to-1 operation.
All the same, I was absolutely shocked that after a few cranks on the starter the truck fired up and ran... but the idle speed was insane and I shut it down immediately.
So from those of you who've done this one or many times before, is this simply a matter of cranking down the idle speed screw or have I done something else wrong? The latter of which I'm completely willing to concede could have happened.
Carb is a Motorcraft 2100 on a 360 FE and I'm happy to fill in any other necessary details if needed.
All the same, I was absolutely shocked that after a few cranks on the starter the truck fired up and ran... but the idle speed was insane and I shut it down immediately.
So from those of you who've done this one or many times before, is this simply a matter of cranking down the idle speed screw or have I done something else wrong? The latter of which I'm completely willing to concede could have happened.
Carb is a Motorcraft 2100 on a 360 FE and I'm happy to fill in any other necessary details if needed.
This is the nylon fast idle cam which may have broken. Originally it was white, but over time, it begins to turn yellow.
2100 cam is the same for all V8: 1964/74 FoMoCo Passenger Cars; 1966/74 Bronco; 1967/74 F100/350 (with auto choke); 1969/74 Econoline.
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Cross-Country
Joined: Sep 2015
Posts: 55
Likes: 1
From: Oregon
Lookat this parts catalog pic between the choke body and carb for 9F577
This is the nylon fast idle cam which may have broken. Originally it was white, but over time, it begins to turn yellow.
2100 cam is the same for all V8: 1964/74 FoMoCo Passenger Cars; 1966/74 Bronco; 1967/74 F100/350 (with auto choke); 1969/74 Econoline.
This is the nylon fast idle cam which may have broken. Originally it was white, but over time, it begins to turn yellow.
2100 cam is the same for all V8: 1964/74 FoMoCo Passenger Cars; 1966/74 Bronco; 1967/74 F100/350 (with auto choke); 1969/74 Econoline.
Or in other words, always reconnect the throttle return spring.
Freshman User
Joined: Sep 2017
Posts: 34
Likes: 0
From: Kenosha, WI
Check that your throttle return spring is installed. I disconnected mine by accident when I installed my electronic ignition and the first time I started it up I had to quickly shut it down as it tried to go to full throttle.
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