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Old 12-20-2021, 06:48 AM
Tonylito Tonylito is offline
230 Tornado
 
Join Date: Nov 03, 2019
Location: Boston
Posts: 13
(another) fast idle question

I did extensive search but have not seen the resolution to this.

Status - new engine, new carb, messy vacuum.

So just did all the adjusts - choke, timing, etc.

The jeep starts and runs better than it ever has.

The idle is set to 650rpm. Read then its idling with timing light.

When you 'drive' the throttle does not return all the way to base idle (650) but rather somewhere around 950-1000rpm.

When I am actually driving the car .... it does to about 20 mphs without me touching the gas. I can hit the accelerating and I cant get it back to 650 idle.

When under the engine .. you can 'force' the throttle back to its 650 position. So it appears the throttle plates are not closing and the throttle is not being pulled back.

When the car is off - it springs right back to the 650 position and isnt hung up.

I have looked for obstructions on the linkage et al and the fact that its only happening when running - think is might be vacuum related.

Cannot do anything to adjust the throttle screw - has no impact.

Thanks in advance.
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Old 12-20-2021, 02:40 PM
johnsonic johnsonic is offline
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Have you looked at the fast idle cam or choke mechanism? Don't know what kind of carb you're running, but if it has an electric choke, can you verify the choke is getting power?
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  #3  
Old 12-20-2021, 08:14 PM
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drcom drcom is offline
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Sounds like a linkage issue. One of them is in a bind.
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Old 12-21-2021, 06:50 AM
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Brynjminjones Brynjminjones is offline
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Have you got the "anti-diesel" solenoid hooked up? Its purpose is to open the throttle a little wider than the mechanical idle position when the ignition is turned on.

It's not strong enough to open the throttle itself, but it will prevent it from fully closing once you've touched the throttle with the ignition on.

If that was hooked up and adjusted to the wrong position, I could see it causing these issues.
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Old 12-21-2021, 05:42 PM
Tonylito Tonylito is offline
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Join Date: Nov 03, 2019
Location: Boston
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1) the choke and fast cam are operating properly - its getting power and opening power (its electric)
2) I disconnected linkage - its not binding.
3) "anti diesel" solenoid .. Is the plunger thing that is in front of the throttle? The throttle plate is not even close to the plunger and I unplugged it. Isn't this the thing that adds some throttle when you turn on AC?
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Old 12-22-2021, 02:42 PM
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tgreese tgreese is offline
 
Join Date: May 29, 2003
Location: Medford MA USA
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Quote:
Originally Posted by Tonylito
1) the choke and fast cam are operating properly - its getting power and opening power (its electric)
2) I disconnected linkage - its not binding.
3) "anti diesel" solenoid .. Is the plunger thing that is in front of the throttle? The throttle plate is not even close to the plunger and I unplugged it. Isn't this the thing that adds some throttle when you turn on AC?
Item 1 - how do you know? Did you measure the settings for the fast idle cam and the choke? Is the choke cover connected to both hot air and electricity? Did you inspect the choke plate while running and see that it is opening fully?

Item 3 - it's an idle stop solenoid. They are used both to boost idle speed with AC or whatever, and to prevent run-on ("dieseling") when the engine is shut off. When used to stop run-on, they are activated always while the key is on. When the engine is shut off, the throttle flaps close completely and kill the engine by shutting off air and fuel.

The carburetor should close down enough to kill the engine. If the idle stop is all the way out and the engine keeps running, you likely have a vacuum leak that provides air to the engine so it keeps running. Or, the carburetor was assembled badly and the throttle plates do not fit tightly in the bores. Or the fast idle cam is holding the throttle open. A closed throttle should kill the engine.

You need to do some simple tests - you can't expect to figure this out with just brain power (even the collected brain power here and at FSJN).
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Last edited by tgreese : 12-22-2021 at 03:08 PM.
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