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Engine RPM sticking at 2000 rpm |
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tomasont
AMC Apprentice Joined: Sep/20/2019 Location: Lenexa, KS Status: Offline Points: 39 |
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Hey Chris,
Did you ever get this issue resolved? I'm really curious how this turned out. Later, Todd |
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Greyhounds_AMX
AMC Addicted Joined: Nov/14/2009 Location: Kansas City Status: Offline Points: 1268 |
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At this point I still have the problem.
I replaced the distributor as it was obviously getting sloppy, replaced the throttle pedal cable with a Lokar, replace the cable bracket with a nice stout aluminum billet piece, added a pair of stronger return springs, and had the brake booster rebuilt by Booster Dewey. I also tore down the carb and checked/adjusted everything there. Last night I figured out what is happening, although it's something I've never seen before. When the car is shut off I can run the throttle by hand and it snaps back closed tightly every time. But if the car is running, the throttle stays where ever I leave it, and doesn't return to the closed position. If I twist it open say 5-10 degrees and get the engine up to 2000 rpm and then let go of the throttle shaft it stays right there. If I do the same with the car shut off it snaps back tightly closed every time. It's like the differential pressure across the throttle blades forces the shaft into the base plate hard enough to create enough frictional force that the return springs can't overcome it. I suppose I could add more return spring force, but it would be really crappy to drive then. With what I have it's already tending to act very "on/off" in nature instead of smooth. With a stick I really want the smoothest throttle action possible. I believe the root cause is the aftermarket primary throttle shaft I used during the initial rebuild. I'm guessing it didn't have the correct anti-friction green coating that the real Holley parts have. I'll probably either replace the base plate completely with a new one from Holley or replace the entire carb if I stumble onto a good deal somewhere.
Edited by Greyhounds_AMX - Sep/28/2019 at 9:45am |
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1968 AMX 390 w/T5
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6PakBee
Supporter of TheAMCForum Charter Member Joined: Jul/01/2007 Location: North Dakota Status: Offline Points: 5454 |
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Hmm. Does this happen with the engine cold (both conditions) or the engine hot (both conditions). I know you know what I'm driving at, thermally driven expansion interference. But that is a long shot, I would think the baseplate would expand more than the shafts, ie the clearance would open up.
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Roger Gazur
1969 'B' Scheme SC/Rambler 1970 RWB 4-spd Machine 1970 Sonic Silver auto AMX All project cars. Forum Cockroach |
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Greyhounds_AMX
AMC Addicted Joined: Nov/14/2009 Location: Kansas City Status: Offline Points: 1268 |
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It doesn't seem to ever change, cold or hot. If I drive it to a cruise night when I pull into the parking lot I'm still fighting with the thing to get the revs to come down.
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1968 AMX 390 w/T5
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PHAT69AMX
AMC Addicted Joined: Jul/07/2007 Location: West Virginia Status: Offline Points: 5903 |
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Did not read it all.
Throttle Blades have tapered edges and specific top & bottom, front and back edges. Was that small detail observed when replaced ?
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Greyhounds_AMX
AMC Addicted Joined: Nov/14/2009 Location: Kansas City Status: Offline Points: 1268 |
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Yep - numbers down on the butterflies. This is really crazy, and not something I've ever seen or heard of happening before.
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1968 AMX 390 w/T5
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