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Fast idle hanging up on my 260 V8 with automatic choke
Do you have the black bakelite / ceramic choke cap? If so it sounds like that is out of adjustment, maybe too much spring tension on it. I've found the best way to adjust it is on a cold engine. The sequence I use is this:
Engine off...remove the air cleaner and open the throttle by hand all the way and release. This sets the choke.
Loosen the three screws that hold the black cap and rotate it until the choke opens....then gradually rotate it in the opposite direction until it closes.
There is a notch on the housing at 12:00 dead center with a bunch of notches to the left and right of it. This a reference for rich and lean. The center on is called 'index'.
Index will usually get you in the ballpark but I've found that these are only a guide as the spring sometimes weakens over time in the cap and certain replacement caps are wound different.
Once you have the cap rotated to where the choke 'barely' closes, regardless of where the notches are, add a little more turn to set a little preload. Now your choke is set.
There is a small fast idle screw on the throttle linkage itself on the passenger side (not the small one screwing into the white plastic piece). You can adjust it to achieve the required fast idle once you fire the engine up. The engine should fire up clean and have enough fast idle to 'clean up' the initial start where the choke is closed.
NOW...that got it closed and started. It now has to heat up and open. If you have the original manifolds there are two pipes that come from the pass. exhaust manifold. Once comes up and with a rubber hose end attaches to the lower portion of the air horn on the carb, the other attaches to the choke housing.
Bssically the choke housing port has a small amount of vacuum on it. It sucks fresh air from the carb fitting in the airhorn, down the pipe through the hot manifold and up and into the choke housing to provide heat to unwind that thermostatic choke coil.
NOW..if you have headers and do not have the pipes in the manifold I would recommend intalling an electric choke cap and running a 12V source to it when the key is on. The rest of the adjustment is the same. Whew! Sorry to be long winded and I didn't even ask you what sort of carb you have. This adjustment basically works on the motorcraft, holley, edelbrock etc. You need spring tension to close it when the throttle is open and you certainly need heat to open it and to 'keep it open' [img]/forums/images/smiles/icon_spin.gif[/img]
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