Stuck idle mixture screw

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friedman
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Stuck idle mixture screw

Post by friedman » Wed Oct 10, 2018 8:44 am

Turns out the 75 spider I just got does in fact have a 34 ADF and as scuzzy as it looks on the outside it's in great shape internally. The only problem is that the idle mixture screw is seriously stuck in the carb base and won't turn in or out. Been soaking it in PB Blaster but does not seem to be doing anything. Any hints?
Carl in Virginia
80 spider
86 Bertone
77 X1/9
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cgranju
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Re: Stuck idle mixture screw

Post by cgranju » Wed Oct 10, 2018 8:52 am

I've been using & appreciating Aerokroil for stuff like this lately.

Is it brass in aluminum? Might take some chemistry to free a bond there? (what chemistry, I don't know)
Chris Granju
sunny East TN
owner of a number of Fiats built prior to 1986
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bartigue
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Re: Stuck idle mixture screw

Post by bartigue » Wed Oct 10, 2018 9:18 am

Csaba suggested to me recently to drip candle wax onto these tight bolts and the paraffin will make its way along the threads. Worked for me on a nasty exhaust manifold. Another excellent penetrant is 50/50 acetone and transmission fluid. Heat may also help here, though I'd be careful to heat the whole body and not just apply a torch to the screw as it may warp the aluminum casting.
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Brad Artigue
1982 Spider 2000
I've restored, worked on, sold, bartered, and bled for:
1970, 1979, 1980, 1981, 1982 124 Spiders -- 1969, 1970 850 Spiders -- 77 X1/9
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friedman
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Re: Stuck idle mixture screw

Post by friedman » Wed Oct 10, 2018 12:57 pm

I thought about heat too and like you wasn't exactly sure how to do this....I suppose the kitchen oven when the wife is out shopping. I'd like a solution I could just drop the whole throttle plate in for a week rather than spritzing PB on it.

I looked at my Weber parts box hoping a throttle assembly from a 32 ADF might work but of course the throttle bores and plates are smaller. Then we have dreams of our best friends with a lathe taking a 32 assembly and making it the same size throttle bores as the 34, moving the throttle plates over, etc etc. But my local friends are useless and don't have lathes.
Carl in Virginia
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86 Bertone
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bartigue
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Re: Stuck idle mixture screw

Post by bartigue » Wed Oct 10, 2018 1:13 pm

A can of Berryman's. The carb base fits right in. Leave it for a week or a month.
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Brad Artigue
1982 Spider 2000
I've restored, worked on, sold, bartered, and bled for:
1970, 1979, 1980, 1981, 1982 124 Spiders -- 1969, 1970 850 Spiders -- 77 X1/9
http://fiat.artigue.com
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friedman
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Re: Stuck idle mixture screw

Post by friedman » Wed Oct 10, 2018 4:29 pm

Is that like the fake carb cleaner in the big can that Gunk now sells in place of the old good stuff?
Carl in Virginia
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bartigue
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Re: Stuck idle mixture screw

Post by bartigue » Wed Oct 10, 2018 9:48 pm

No
Berrymans is the real deal, stinky, pollutes, works wonders, lasts forever.
-----------------------------------------------------------
Brad Artigue
1982 Spider 2000
I've restored, worked on, sold, bartered, and bled for:
1970, 1979, 1980, 1981, 1982 124 Spiders -- 1969, 1970 850 Spiders -- 77 X1/9
http://fiat.artigue.com
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rridge
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Re: Stuck idle mixture screw

Post by rridge » Thu Oct 11, 2018 6:42 am

There's not a lot, including my lungs, that will stand up to aerosol brake cleaner, the original and highly flammable kind. Differential expansion and contraction is also your friend.
Richard
'81 Turbo Spider
Rockville, MD
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friedman
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Re: Stuck idle mixture screw

Post by friedman » Thu Oct 11, 2018 8:23 am

Richard, I need something I can soak the part in, brake cleaner is a spray. Brad I'll see if I can find that toxic stuff.
Carl in Virginia
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86 Bertone
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fp55scca
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Re: Stuck idle mixture screw

Post by fp55scca » Thu Oct 11, 2018 6:48 pm

friedman wrote:
Wed Oct 10, 2018 8:44 am
.....the idle mixture screw is seriously stuck in the carb base and won't turn in or out. Been soaking it in PB Blaster but does not seem to be doing anything. Any hints?
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--I suspect that should be a brass mixture screw in an aluminum housing, but I suppose the mixture screw could be steel as well? If you're lucky, you just have corrosion holding the screw. If unlucky, someone may have cross-threaded the wrong mixture screw into the housing, in which case you're screwed (no pun intended).

--Lots of good penetrants have been recommended here, as well as the application of heat. If it's just corrosion holding it, you may also try using a small tack hammer to tap the mixture screw squarely and lightly. Then try, alternately tightening the screw, followed by trying to loosen the screw. This sometimes works for delicate stuff.
Jim Scurria
Norfolk, VA

1972 Fiat 124 Spider
1971 Spider - SCCA FP-24
1974 Fiat 124 Spider
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