VROOOOOOOOOOM... wont slow down

Started by Chris Braun, February 15, 2006, 07:05:07 PM

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Chris Braun

my 60 Cadillac Sedan, among other problems, just started this habit of staying revvved up after a trip.  It started good the last 4 days, idled high from the choke, then after a quick vroom on the gas, it idled normal, and drove fine.  Upon exiting the highway, the sucker wouldnt slow down!!!!  Popped it into neutral, and stopped just fine, but she was idling FAST.  Hit the gas pedal a few times, NO CHANGE!!!  still idling faster than ever.  I got out, removed the air cover, and cranked down all three screws on the carb, until they were ALL THE WAY CLOSED!!!  sucker still was idling high.  I went back into the car.  I pulled on the gas pedal, that finally slowed things down, but as soon as I let go... VROOM  back up again.  Ive replaced the throttle return spring within the last week, as I thought that could be my problem. But thats not helping.  Something else is causing this mess....

any ideas???

Doug 22747

Sounds like youve got that Carter carb.  I never had any luck with that carb idling smoothly.  Anyway, it sounds as if youve got a vacuum leak somewhere.  Begin by checking hoses, then gaskets.  You should also adjust the choke (a little leaner), and assure that the linkages, etc., are free and operate correctly.  And just for the heck of it check the timing.  Its possible that the chain jumped.  Good luck Doug

Bruce Reynolds # 18992


Sounds like a mis-adjusted throttle linkage, as you mentioned that it will idle down when you pull the pedal back.

Doug is on the right track as well, in as much as a vacuum leak can cause a problem.

Now, your car has the automatic parking brake release, so that when the gear lever is in park, the vacuum to the parking brake is turned off, and when you put the gear lever into a driving gear, the vacuum is sucking from the parking brake "motor".   If the vacuum hose is missing there, that will give you a leak, but not that much to cause you makor drama, but every leak is a leak.

The Tassie Devil(le),
60 CDV

denise 20352

   When its idling fast, is the stop on the linkage actually contacting the idle speed screw?   Does the idle slow down if you push the throttle shut against the screw, at the carb?  If it does when you pull the gas pedal back, I would assume so.

   This sounds like a sticky linkage to me.


Geoff Newcombe #4719

I would also check to make sure the automatic choke linkage hasnt broken or come loose allowing the fast idle cam to "float" and cause the car to go to fast idle when it is not supposed to. Also, if, as you said, you turned the 2 idle mixture screws and the larger air screw all the way in, the car will not run at idle at all until you back them back out to an approximately correct setting and then fine tune it as per your manuals instructions with a tachometer.  Turning those screws in when the engine is racing does nothing because the engine isnt running on the carburetors idle circuit which is what those screws adjust and control.  Let us know what the outcome is.

Paul W Allen CLC #20193

Check for bent throttle plates. Did you really stomp on it hard at some point? I have seen the carb throttle plates get bent from this. If theyre bent open slightly the car will race in the idle position. Its not likely, but a possibility.

53 Coupe
Twin Turbine

denise 20352

  Umm...good point...I think we might need more information about these three screws.

  If you turned the idle screw in (clockwise), then you have set the idle speed to its maximum.

  If you turned the mixture screws all of the way in (also clockwise), then your engine wont idle because you have leaned the mixture all of the way out.


Ed Dougher

I agree with Denise.  Id first try to loosen things up with a squirt of Gumout.

Chris Braun

Ok.. so far, Ive cleaned the carb up pretty good, linkages appear to be moving freely, and I checked the vacuum connections and hoses.  Hoses are pretty old, have a few little cracks in them, so I think its time to replace them.  But..  I hardly think a vacuum problem could cause all this mess.  Im curious about the idle screws, as Ive always thought when they were in, that is turned clockwise into the carb, they slowed the idle down.  Same for the main screw.  Im pretty sure the main used to be able to cause the engine to idle on down until it stopped running.  I remember setting the idle in gear at about 250rpm once, just to prove it would idle that slowly, but I normally had it set at about 600 or so.  Then with it running bad, Ive slowly been adjusting the idle speed up, to compensate for worn rings or whatever.  Before this mess started with it really revvin up, I had the idle set at about 1000 rpm.  Which had me shifting to neutral to stop already.  So.. when it started racing after a trip, I had no trouble putting it in neutral to stop, but I figured the rpms would come back down, and they havent.  Even after letting it sit a few days, after cleaning it up, its still not running any slower.  Itll start and run, at about 2000rpms, with all three screws turned completely clockwise into the carb.  Makes NO sense to me at all.  Im still going to check the linkages again, and make sure to replace the hoses, perhaps Ill spray some more cleaner on, and make sure something isnt gunked up.  Any other suggestions, greatly appreciated :)