What do you think happened?

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Bl1zzard

Bl1zzard

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We drove the car to the last car show of the year and when we got there it was idling ~about 3000 RPM. It's been fine all summer and I haven't touched it. I have to back off the throttle cable adjustment almost a half inch to settle it down to normal. How on earth did I lose almost a half inch of adjustment? Still scratching my head on this.

1974 Dodge Dart Swinger with a 360 LA and Holley 750 DP. Nothing crazy about the set up. Lokar throttle cable and kickdown. Been in place for over 3 years.
 
mopar56 said:
I agree with Dana 67, I'd check your carb to manifold bolts, bet there loose or you blew through the base gasket
Click to expand...
Or maybe the pcv is wide open, hose slipped off, brake booster has a gaping hole.
 
That would explain the high idle, but not how the cable came out of adjustment by a half inch, and readjusting the cable rectified it. A cable adjustment will not compensate for a vacuum leak.
Follow the linkage/cable/pedal route, make sure there's no binding/ interference anywhere. Check the cable for kinking or binding- a frayed cable can hang up inside the housing, or on the ends... Pay close attention to where the cable enters the cabin and connects to the pedal linkage for anything that may have popped loose or is otherwise out of whack.
 
And for a real "DOH!" moment, I've had the floor mat bunch up against the pedal and not let it return to idle... :BangHead:
 
When you floor it, the cable pulls on the throttle. When the throttle stops at WOT, and the gas pedal is not yet on the floor ; then if the anchor-clamp is just loose enough, the cable can slide forward. You might have/ should have, felt that .
However, with the cable slid FORWARD, it would now park with slack in it! If this happens to you, then your cable is the wrong length for your geometry, or the other way around.
But this has nothing to do with the changing idle speed. This would require the cable to move backwards in the clamp towards the firewall, or the carb to move towards the rad away from the anchor, neither of which is a realistic possibility. So IDK what happened.
About the only things I can think of is that the cable is not running back out of the sheath. This would make your pedal sit lower than usual, or the pedal weld is separating, or like mentioned, the simplest of all is that the carpeting or something is bunched up on the cable inside the cabin.
 
I've seen a cable wrapped around the throttle arm, the bracket bent, sticking from a fray...

If you could ...as you said " add a 1/2 inch of slack to the cable"
Then It's not a vac leak, It's an adjustment issue.
The throttle would be in the mains @ a half inch, makes sense @3000rpm.
 
Professor Fate said:
And for a real "DOH!" moment, I've had the floor mat bunch up against the pedal and not let it return to idle... :BangHead:
Click to expand...
It seems that the simplest solution is usually the correct one. Glad it is OK and it did not stick wot on you.
 
Is it possible the adjustment just slipped?
 
Sorry for not responding. You are all on the right track, something slipped/opened up. I haven't been able to really look at it much here, cold, snowing, lazy. I did pull the plugs and they are black, I've been checking them all summer since we rebuilt the engine last winter. They've been nice light brown/gray all year until that last road trip. It's running really rich. I need to warm it up and do a complete check of the timing, vacuum, etc. Then I'll have a better idea of what's going on with it. Thanks for all the suggestions.
 
Finally got some time to warm it up and check the timing and vacuum. It's all good, sitting at 20 degrees @ 800 rpm pulling 15 inches nice and steady. No vacuum leaks, the engine is happy with that timing, no pinging under load and idles well.

I'm pointing to the carb. It's a hand me down from my cousin. Holley 750 DP. Gotta be at least 30 years old. I've put in a rebuild kit, but I'm not sure it's really up to snuff. Weird things like the front passenger side idle screw has to be in all the way or it just stumbles at idle. I'll go on the hunt for a known good used or a new carb this winter. Suggestions?
 
Back around 78-79 I had a 70 Charger R/T do something similar, I stood on the gas & wound it up pretty tight... When I tried to slow down the engine idle was at 3500.... Turns out the drivers side mount broke & the engine torqued over so far it pulled the throttle cable housing out of the metal ferrule at the firewall...
 
Had one this summer, take it for a ride and would come back with idle a 3000 rpm. The idle adjustment was turning in on it’s own. Little to long the spring was not holding it. Put a new shorter one in and all better!
 
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