Hey Dan & Tophat
Have you tried the light duty lock tite or even nail polish. Just a thought. Although I think Dans problem is junk in the fuel/fuel system. Ive seen trash get caught on the seat or needle. Tune it up then run, all of a sudden trash goes thru and you have to retune.
BTW Pretty Dart.
Frank

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Scrapple: Because a mind is a terrible thing to waste.
73 Duster - Race Car
66 Dart Wagon - DD
178" FED
82 D150
All Slant powered

Scribe or make a fine mark on the screws (as a reference point), drive as usual, then recheck to see if they actually are moving.

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<img src="http://farm4.static.flickr.com/3173/2992308402_5481afb26e_t.jpg">

Well, I do routinely remove the plastic mixture screw limiter caps from '69+ carbs. This allows full-range adjustment, but also takes away a stop on the mixture screw. A "safety wire" type arrangement (wire clip thru the screw slot or a new hole drilled in the screw head) would probably work fine as a retainer, but no such retainer should be needed. I have in the past wrapped the upper threads of the mixture needle with Teflon tape, and that's worked well, but it's really just helpful where the mixture needle turns too easily in the throttle body. This one's nice and firm. There's no trash in the fuel or carburetor — and if there were, the idle might've suddenly gone lean, but not rich. I will keep an eye on it and see what develops or if it's a one-off.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

In the neighborhood of 6.
Maybe this is one of those brand preference issues... for example:

I pretty much despise Fords in general, I've never owned one that ran properly, no matter how much work I did to it. Had a Mustang, did all the tuneup procedures with new parts, etc etc, it blew both headgaskets, and fried the C4 within a month following that. My Bronco II blew the engine at 129k miles, and my F-150... well I got rid of that before it had a chance to die.

Same may go for Carbs, I am preferenced toward Holleys, and everytime I get a carter (aside from the BBD) they fail miserably on me.

Maybe it's all in my head...

PM me your info, and I will round those Carters up.

~THOR~

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1984 D100 Shorty Custom
Certified Auto Appraiser - RevItUp Classic Appraisals
President - Cherry City Bombers CC
Part of Tyrde-Browne Racing

Long shot: try a valve adjustment? That can certainly give poor/rich idle and symptoms you describe. Hard to see how it would come on fast, but worth a look. Did the weather get warmer, thus causing hotter temps and thus tighter lash?

Lou

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Home of Slant6-powered fun machines since 1988

Nope. Valves are adjusted fine. Again: The idle cleaned up just fine with an adjustment of the mixture screw (clockwise).

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Anothor 'vote' for some junk or build-up around the idle air/fuel needle screw... as soon as you move it a little, the crap "moves along" and the idle circuit starts workig better.

I just had this happen with our 66 Dart, it just started runng 'choppy'.
I re-adjusted the idle A/F and everything was back to normal... it ended up about 1/2 turn "out" more then it started but seemed "happy"... so that is where we left it.

I pulled the valve cover and "ran" the valve lash anyway... no real changes were needed there.

<shrug>....

In the case of my 900,000 km work truck things like that are just part of the day-to day. You realize your vehicle is in a constant state of flux and that you can never get your head around the hole picture for more than minutes. Eureka moments are few and far between.....and funky stuff just keeps on happening.

Its OK to not know whats actually happening if you can fix it or at least get home....

The least you can do is hang some crap off your mirror as a Talisman to the God of High Performance and Good Gas Mileage.

That little string of Kootenay beads has saved my butt countless times. The evildoers hate it.

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Yeah....Im the one who destroyed this rare, vintage automobile.....

Unless I'm misreading previous responses, yours is the first vote for crap on the idle needle, tho we had a couple votes for an inlet needle (float valve) problem. Anyhow, yep, I pulled the idle needle and turned it tip-first into a twist of paper towel, and came away with a nice big smudge of rust. Oh, ask me how much I love the fact that our gasoline is cut 10% with alcohol. I used up the rest of a can of carb cleaner blowing out the air bleeds and the idle bypass airway, readjusted the idle mix, and everything seems a lot happier — no more misfiring, and much cleaner-smelling exhaust (Mm-mm-good! ). We'll see how long it lasts.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Phaw. Easy for you to say…you probly snuck thru Toronto on a tipi run, found my Dart parked in the street, jimmied open the hood and richened my idle mixture in the dead of night, just to mess with me!
Reed was right; I should've kept the dashboard chicken.

(Edit: With this post right here, I'm at 15 kiloposts! )

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

On my motorcycle, I put a blob of RTV on the idle mixture screw and spring to keep it from backing out.......

I also think a split lock washer would work (between spring and screw)

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

no one sneaks through Trauna......

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Yeah....Im the one who destroyed this rare, vintage automobile.....