Before diving into the carb you should do some other diagnostics. Do you have a vacuum gauge? You can check the idle mix with one, but if not you can do it by ear. Here's how I do it:
- With the engine off gently screw both idle mix screws all the way in, counting how many turns they were turned out. Accuracy to 1/8 turn is accurate.
- Then turn them out 2 1/2 turns each.
- Attach the vacuum gauge to a port on the manifold. One of the ports on the plastic manifold back on the firewall will work also. But whatever you use has to have full vacuum at idle.
- Start the engine and warm it up, and then turn the idle mix screws out 1/4 turn. If the vacuum or RPM increases, then turn them out 1/4 turn more, and continue that until the vacuum/RPM quits increasing and starts to drop. But if the vacuum/RPM actually dropped when you turned the screws the first 1/4 turn out, then start going in 1/4 turn at a time until you find the best idle.
Assuming that you find a good idle then you may not need to rebuild the carb. But if turning the screws all the way in gives a better idle, albeit not really good, then your power valve is leaking.
And if turning the screws all the way out gives a better idle then you probably have a vacuum leak, like a cracked vacuum hose.
Anyway, give that a try and we will see where to go next.
Gary, AKA "Gary fellow":
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Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI
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