Engine running at 3k rpm on startup.

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SFBay‘72Duster

SFBay‘72Duster

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Looking for some help with my ‘72 Duster with a 360 and an a Carter AFB 4 barrel carb.

I was recently under the dash replacing the brake light switch. It was a total pain in the a$$. I had to remove a lot of stuff to got to it.

Once I had it all buttoned up I went to start it and the idle was super high like I was pressing on the throttle. It is about 3k rpm. I didn’t mess with the carb at all. Idled fine last time I started it about a month ago.
I have an aftermarket gauge cluster and there were a lot of wires blocking access to parts I needed to remove to get to my brake switch. There is also a vacuum hose coming off the back of the carb and into the firewall. I’m assuming that is for the rpm gauge. Maybe I knocked it off causing a vacuum leak?

I checked my electronic choke and it’s getting power and the adjustment is good. My fast idle screw was a bit off but throttle cables are in good shape and seem to be functioning correctly.

Any insight would be much appreciated. Was looking forward to driving it but oh well. The struggle continues
 
Any vacuum hose coming in is for a vacuum gauge. An open vacuum will result in a high idle.
 
My guess is my accidentally altered something to do with the gas pedal. I'd smoke it over real good.
 
thank u for the reply. I don’t have a vacuum gauge on my dash so maybe that is my issue. Maybe it was blocked off and I needed with it by accident. Would that make my idle this high though? I pushed the throttle a bit and my rpm’s got stuck even higher.
 
The vacume hose might be for AC actuators.

Easy to test. Pinch it off by the carb and retest.

My best guess is you inadvertantly did something to the gas pedal and throttle linkage.

Another easy test. Remove the throttle linkage from the carb. And because rd the butterfly scare closed
 
Took a look at my gas pedal and it looks like the cable is rubbing on the hole through the gas pedal mount. Doesn’t seem to be causing rpm issue though but does anyone know where I can get a new rubber grommet?
 
Excuse me if I sound like "Joe Obvious", but did you bunch up the floor mat under the gas pedal while you were rootin' around under the dash?
 
I looked at the fast idle cam. It wasn’t touching the screw on the throttle. I adjusted it but no change.
I’m not very experienced with carborators and I can’t find any information on tuning or troubleshooting an old Carter AFB carb. Any one have suggestions?
 
Here are some pics of my carb. I know it’s dirty don’t judge me I’m working on it. :/

IMG_3332.jpeg


IMG_3331.jpeg


IMG_3330.jpeg
 
I believe this is tha fast idle cam. Not sure if the orientation is correct. There is a few ways it can touch that screw

IMG_3331.jpeg
 
SFBay‘72Duster said:
thank u for the reply. I don’t have a vacuum gauge on my dash so maybe that is my issue. Maybe it was blocked off and I needed with it by accident. Would that make my idle this high though? I pushed the throttle a bit and my rpm’s got stuck even higher.
Click to expand...

In post #5 you said you pushed the throttle and the rpm got stuck higher .
Sounds like you have a throttle problem .
Any vacuum leak would not act that way .
You need to check all of your throttle linkage,,,somewhere nearby that will rest your culprit .

Tommy
 
The fast idle screw is on the fast idle cam because the choke is in the start position. In post #14, you can see the choke blade is at an angle. Once the engine warms up, the choke mechanism [ round black ' thingy', with the red wire on it ] should pull the blade to the vertical position [ vert: engine at operating temp ]. If this is not happening, then that will be causing the fast idle & needs to be investigated.

In the top pic in post #14, you can see the idle speed screw, just next to the spring arm. A tang should contact that screw once operating temp is reached.
 
So looked at my accelerator Pedal a bit more and it looks like the mount is a bit off. When I push my pedal the fire wall flexes. Also the cable is rubbing on the hole through the fire wall. The grommet is all blown out. Is that rubber pice part of the cable assembly or the mount?
 
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Thank u to everyone who gave me advice. It ended up being the throttle cable. There is a bracket on top of the intake manifold that clamps it in place. Looks like that got loose some how
 
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