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Author
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Topic: Engine not returning to idle
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birbor
Journeyman Posts: 4
From: Vancouver, BC, Canada
Registered: Aug 2005
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posted 08-12-2005 02:11 AM
 
Anyone have any advice on why my 289 engine in a '68 Mustang coupe with a 2100 Autolite carb doesn't return to idle once I take my foot off the gas pedal? I've owned this car for 28 yrs and fixed many of the problems, but I'm having trouble with this one. I tried adjusting the accelerator linkage, but this linkage looks okay, although I'm not 100% sure. Is it possible the choke is somehow keeping the throttle open? The problem seems to happen when the engine is hot, especially when it's hot outside. Also, should there be only one tube running from the passenger side exhaust manifold to the choke assembly? - should there be a return tube? Any suggestions would be much appreciated. Thanks. Biraj
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Fastymz
Moderator Posts: 22791
From: Reno Nv M&M #1240
Registered: Apr 2001
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posted 08-12-2005 02:13 AM
Yes, on the one tube.
Is the throttle return spring good? If you unhook the linkage while it's acting up does the idle go down?------------------
oddly obsessed with big scoops on little Mustangs 65 coupe 351w C4 Big Boss 429 hood scoop,8" 3.40 TracLoc. My Pics
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Mike W
Gearhead Posts: 135
From: CA
Registered: Jul 2003
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posted 08-12-2005 03:20 AM
There should be a second tube to the exhaust manifold for a filtered air intake. I used to hate those tubes. They were one of the first things to break off. An electric choke made life easier.  Check your linkage for any binding. If the choke is not causing the high idle, a helper spring may do the trick. At least you won't need a computer. I ran my 65 for years without a choke plate. I installed a manual choke cable to the choke fast idle linkage so when the engine was cold, I could run it at a fast idle. After it warmed up, I would push it in to get a normal idle speed. This would only work in a moderate climate.
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Scott H
Gearhead Posts: 1480
From: Chicago area
Registered: Mar 2005
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posted 08-12-2005 08:41 AM
Yes, there are two tubes going to the exhaust manifold.
One tube connects to the top of the carb with a short piece of rubber hose. It takes filtered are from under the air cleaner and routes it to the bottom of the exhaust manifold.
From there the air travels inside a small cavity/tube inside the manifold and gets heated up.
Then the other tube carries the filtered heated air to the choke thermostat.
There is a small brass piston that controls the choke opening and closing, and it is very susceptible to dirt and contamination, usually caused by unfiltered air coming in through the choke tubes. If the piston is binding or sticking it may keep your choke linkage from allowing the car to return to idle.
You can dis-assemble and clean the choke housing and linkage while it is still on the car and I think that might solve your problem.
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birbor
Journeyman Posts: 4
From: Vancouver, BC, Canada
Registered: Aug 2005
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posted 08-12-2005 10:59 PM
quote:
Originally posted by Fastymz:
Yes, on the one tube.
Is the throttle return spring good? If you unhook the linkage while it's acting up does the idle go down?
Hi. Thanks for the feedback. You're right. Interestingly, it was the return spring. I took it to a Ford dealer and they installed a new bracket on the intake manifold and hooked up a brand new, stiffer spring. They also left the old one where it was. My car runs great now. Thanks for your help. Much appreciated. Biraj
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birbor
Journeyman Posts: 4
From: Vancouver, BC, Canada
Registered: Aug 2005
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posted 08-12-2005 11:01 PM
quote:
Originally posted by Scott H:
Yes, there are two tubes going to the exhaust manifold.
One tube connects to the top of the carb with a short piece of rubber hose. It takes filtered are from under the air cleaner and routes it to the bottom of the exhaust manifold.
From there the air travels inside a small cavity/tube inside the manifold and gets heated up.
Then the other tube carries the filtered heated air to the choke thermostat.
There is a small brass piston that controls the choke opening and closing, and it is very susceptible to dirt and contamination, usually caused by unfiltered air coming in through the choke tubes. If the piston is binding or sticking it may keep your choke linkage from allowing the car to return to idle.
You can dis-assemble and clean the choke housing and linkage while it is still on the car and I think that might solve your problem.
Hi. Thanks for the feedback. You're right about the helper spring. As mentioned in my email to fastymz, I needed better return spring power on the accelerator linkage side. I was wrong about thinking that the problem may be related to the choke heat tube. Thanks for the feedback. Much appreciated. Biraj
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birbor
Journeyman Posts: 4
From: Vancouver, BC, Canada
Registered: Aug 2005
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posted 08-12-2005 11:06 PM
quote:
Originally posted by Scott H:
Yes, there are two tubes going to the exhaust manifold.
One tube connects to the top of the carb with a short piece of rubber hose. It takes filtered are from under the air cleaner and routes it to the bottom of the exhaust manifold.
From there the air travels inside a small cavity/tube inside the manifold and gets heated up.
Then the other tube carries the filtered heated air to the choke thermostat.
There is a small brass piston that controls the choke opening and closing, and it is very susceptible to dirt and contamination, usually caused by unfiltered air coming in through the choke tubes. If the piston is binding or sticking it may keep your choke linkage from allowing the car to return to idle.
You can dis-assemble and clean the choke housing and linkage while it is still on the car and I think that might solve your problem.
Hi. Thanks for the feedbak. As mentioned in my feedback to "fastymz", more return spring power did the trick. Your information on the second tube is useful as I wasn't sure about the second tube. I have an "open" air filter in my car, so I don't have that second tube. But I will check the bottom of the exhaust manifold for the second opening. Thanks for the feedback. Much appreciated. I'm thrilled about the problem being solved, and just as thrilled about the feedback. Really great of all of you to reply. Thanks. Biraj
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Scott H
Gearhead Posts: 1480
From: Chicago area
Registered: Mar 2005
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posted 08-12-2005 11:31 PM
quote:
Originally posted by birbor:
I have an "open" air filter in my car, so I don't have that second tube.
The tube doesn't actually attach to the air cleaner housing, it uses a short piece of rubber tubing to attach to a port on the carb. Look on the passenger side of the carb, on the air horn (top piece) just behind the choke. You should see a tube that starts above where the air cleaner sits and goes down thru the air horn so that there is a little tube sticking out underneath. This is what the second choke heat tube attaches to.
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Fastymz
Moderator Posts: 22791
From: Reno Nv M&M #1240
Registered: Apr 2001
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posted 08-13-2005 03:49 PM
quote:
Originally posted by birbor:
Hi. Thanks for the feedback. You're right. Interestingly, it was the return spring. I took it to a Ford dealer and they installed a new bracket on the intake manifold and hooked up a brand new, stiffer spring. They also left the old one where it was. My car runs great now. Thanks for your help. Much appreciated. Biraj
I'm gald to help 
Now go for a nice drive.
------------------
oddly obsessed with big scoops on little Mustangs 65 coupe 351w C4 Big Boss 429 hood scoop,8" 3.40 TracLoc. My Pics
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