1977 Ford Bronco rough idle. Smooth at high RPMs

Tiny
KROWENS76
  • MEMBER
  • 1977 FORD BRONCO
  • V8
  • 4WD
  • AUTOMATIC
  • 177,000 MILES
This just started yesterday leaving work. Engine will run rough when ideling(when I say rough, I mean it shakes the whole truck), but as soon as you give it enough gas either driving or in park it smoothes out. The engine doesn't die, but seems as though it wants to. I rebuilt the carburetor 6 months ago and adjusted the timing. And it has run perfect until this point. The engine was recently rebuilt 1 yr ago as well and the following replaced: New spark plugs, wires, cap, rotor, coil, fuel filter, fuel pump.
The temperature has just recently dropped a considerable amount as well (-20°), not sure if that impacts any thing. Another thing I recently noticed is that if I punch the gas, every once in awhile the engine will backfire. This is my daily driver. Please help!
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Tuesday, October 28th, 2008 AT 8:43 AM

4 Replies

Tiny
DLOBI
  • MEMBER
That sounds an awful lot like a vacuum leak. Did any vacuum hoses fall off, fail, get bumped? There is a lot of vacuum in the manifold at idle and little to none as your rpm gets high thus the possible reason it smothes out. Get under the hood with it idling and listen for the vacuum leak.
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Tuesday, October 28th, 2008 AT 8:47 AM
Tiny
KROWENS76
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I tried that. The whole engine is loud and it is hard to tell. Is there another solution to finding a leak? Maybe soapy water? The colder weather wouldn't affect the idle. Resulting in adjusting the carburetor for the change in temperature? Also, would it be beneficial to upgrade to a edelbrock 600 cfm to improve performance?

Thanks!
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Tuesday, October 28th, 2008 AT 8:54 AM
Tiny
DLOBI
  • MEMBER
There are a couple of methods for finding a vacuum leak. Spraying some carb cleaner that can get sucked in the leak will quickly change rpm and let you know. You also can try with a length of hose with one end up to your ear like a stethescope. Move the other end around and you will hear more localized noise this way. Listen for a sucking air sound.
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Tuesday, October 28th, 2008 AT 9:05 AM
Tiny
KROWENS76
  • MEMBER
I have to get to and from work. Is this harmful to my engine to drive until I get it figured out?

Also, would a 600cfm edelbrock carb be a beneficial upgrade? From a performance standpoint?

Thanks
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Tuesday, October 28th, 2008 AT 9:39 AM

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