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Any AFB gurus here?? |
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BU1
AMC Addicted Joined: Aug/11/2016 Location: MN Status: Offline Points: 1973 |
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Posted: Oct/03/2022 at 7:37pm |
Having an odd issue with an 68 AMX AFB where the throttle is slow to return to idle. With the motor off and the linkage disconnected, the springs on the carb are enough to close the throttle just as they should. But with the motor running, the throttle is noticeably a bit stiffer to open, and the carb springs now will no longer close the throttle. RPM's will hang wherever they are when you let go of the butterfly. You have to manually push the throttle closed. What would cause the primary throttle shaft to act tight with the motor running???
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AMO #2726
#1 1968 AMX Rally Green 343 Z code 4spd since 1975 #02642 #2 1968 AMX Rally Green 290 N code 4spd since 2019 #02959 |
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mmaher94087
AMC Addicted Joined: Apr/01/2008 Location: Arizona Status: Offline Points: 1676 |
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This sounds like a warped throttle shaft. It probably occurred with a backfire through the carb. Replace the throttle shaft.
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Mike
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BU1
AMC Addicted Joined: Aug/11/2016 Location: MN Status: Offline Points: 1973 |
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Don't think so. Warped shaft should be sticky at all times, no?? This one only sticks with motor running.
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AMO #2726
#1 1968 AMX Rally Green 343 Z code 4spd since 1975 #02642 #2 1968 AMX Rally Green 290 N code 4spd since 2019 #02959 |
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troutwilly
AMC Addicted Joined: Sep/14/2007 Location: Carriere, MS Status: Offline Points: 991 |
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What if the motor is running but the throttle cable is disconnected? That scenario was not covered. May be a problem with the throttle cable.
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Bill O.
70 AMX |
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mmaher94087
AMC Addicted Joined: Apr/01/2008 Location: Arizona Status: Offline Points: 1676 |
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The 4-speed, AEB, has a dashpot to slow the closing of the throttle but beyond that, I can't think of anything that would cause the throttle to hang up. I'm back to a warped throttle shaft.
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Mike
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FSJunkie
AMC Addicted Joined: Jan/09/2011 Location: Flagstaff, AZ Status: Offline Points: 4741 |
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The throttle body of any carburetor can warp and create a misalignment of the throttle shaft bore. Overtightening the mounting studs usually causes it. The warp can change as the carburetor heats and cools during operation.
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1955 Packard
1966 Marlin 1972 Wagoneer 1973 Ambassador 1977 Hornet 1982 Concord D/L 1984 Eagle Limited |
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mixed up
AMC Addicted Joined: Jun/16/2015 Location: Monroe mich Status: Offline Points: 2156 |
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check all the linkage on the chock side and have you had carb off recently were gasket might be a trouble
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69 amx 290 auto
65 220 290 4spd 80 ford fairmont |
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sweatlock
AMC Addicted Joined: Apr/28/2014 Location: Largo, FL Status: Offline Points: 3285 |
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Don’t laugh but you can have the AFB carburetor base gasket mounted back to front - the hole diameter between the primaries and secondaries on a Carter AFB are very close to being the same size. If you mount the gasket backwards, the secondaries will stick.
Edited by sweatlock - Oct/04/2022 at 6:18am |
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BU1
AMC Addicted Joined: Aug/11/2016 Location: MN Status: Offline Points: 1973 |
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68 has throttle linkage, no cable. Linkage is disconnected as stated in my original post.
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AMO #2726
#1 1968 AMX Rally Green 343 Z code 4spd since 1975 #02642 #2 1968 AMX Rally Green 290 N code 4spd since 2019 #02959 |
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BU1
AMC Addicted Joined: Aug/11/2016 Location: MN Status: Offline Points: 1973 |
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[QUOTE=mmaher94087]The 4-speed, AFB, has a dashpot to slow the closing of the throttle . QUOTE]
FTW!!!!!! I thought when I installed the carb that I had the dashpot adjusted so it would not come into play. I was wrong! It was contacting ever so slightly at the very end of throttle travel. But, the throttle still hangs with the engine running and the throttle linkage disconnected. Turn the engine off, and you can watch the throttle close on it's own. Never seen a carb do that. It's all good though, as the throttle returns properly now with the linkage connected.
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AMO #2726
#1 1968 AMX Rally Green 343 Z code 4spd since 1975 #02642 #2 1968 AMX Rally Green 290 N code 4spd since 2019 #02959 |
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