77 ford 460 idle issues

[npk]

i have a 1977 ford 460 engine. runs great down the road. she is a very hard starter when she is cold, lots of pedal pumps to get her going. she idles like she has a huge cam while cold and after driving 50 miles. the weird thing is that every so often at a stop light or when i park it idles completely smooth.

i was thinking it is a vacuum leak that occasionally seals itself. the problem with that theory is i have plugged all vacuum ports while parked and it still idles rough. my second theory is that it is something with the ignition or timing but i don't know where to start looking.

can a carburetor cause this type of behavior? any suggestions on how to diagnose and fix?


thanks

additional details: this is a stock engine out of a 77 ford van. the only non-factory components are the edlebrock carb (8867) and the adapter plate to attach it to the ford intake manifold.

 

[DNFXDLI]

Choke possibly?

 

[npk]

The choke is electric and unplugged. I could blame the cold rough idle on that but not the rough idle after warm up.


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[DNFXDLI]

Have you checked the static timing?....have you checked the cap, plugs wires?

 

[npk]

No I haven't. I am out of town at the moment. Just trying to form a game plan before I get back and start to work on it. I am hoping to get some info on things that can cause these symptoms that come and go.

Static timing: could being out of time cause this? If so, does it suggest the timing is too advanced or retarded?

Plugs: I have never had plugs fail and then start firing again

Cap & rotor: what do I look for?

Coil: could the voltage be low in the coil and occasionally increase and make the symptoms go away?


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[DNFXDLI]

No I haven't. I am out of town at the moment. Just trying to form a game plan before I get back and start to work on it. I am hoping to get some info on things that can cause these symptoms that come and go.

Static timing: could being out of time cause this? If so, does it suggest the timing is too advanced or retarded?

possibly.....but verifying that it is correct is a start.

Plugs: I have never had plugs fail and then start firing again

worth checking...possibly cracked porcelains or wire that fails due to vibration or temperature

Cap & rotor: what do I look for?

Look for carbon tracking in the cap...worn contacts in the cap...corrosion of cap contacts...same deal with the rotor...look at the brass

Coil: could the voltage be low in the coil and occasionally increase and make the symptoms go away?

again...possibly....a crack in the case or an intermittent contact with the internal wiring

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again...possibly....a crack in the case or an intermittent contact with the internal wiring

 

[npk]

Thanks so much. I will update next week when I get back


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[Workin' Rig]

Honestly, sounds to me like plug wires, OR brain box.