what does this screw do? *pic*

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Jan 8, 2004
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Santa Rosa Valley, CA
Pighead said:
That's one screw I do Know, Idle mixture screw.
That's the idle mixture screw? Then what I REALLY need to know now is this... What is the screw that is at 9 o'clock if that picture is oriented so that the gold screw facing us is at 6 o'clock. It's the screw that faces the firewall. I'm pretty sure that the screw in the pic faces the head. I thought that one was idle/mix.

Man, do I love working on this car in the middle of the night.

Thanks!
 

honk

 
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fyton2v said:
That's the idle mixture screw? Then what I REALLY need to know now is this... What is the screw that is at 9 o'clock if that picture is oriented so that the gold screw facing us is at 6 o'clock. It's the screw that faces the firewall. I'm pretty sure that the screw in the pic faces the head. I thought that one was idle/mix.

Man, do I love working on this car in the middle of the night.

Thanks!

Huh? I've read that sentence three times but don't think I understand what (tf) you're talking about. Nevertheless, YES, the screw facing us all adjusts the fuel mixture at idle only. It doesn't do anything else.

There is no adjustable screw that faces the firewall on my carburators but maybe yours has one. What mine do have are screws (one per carb) that adjust the idle speed ONLY (engine warm), and another which adjusts the FAST idle speed which ONLY has effect during the warming period while the choke is on (engine cold).

The idle speed screw is located lower than the fast idle screw and acts upon a portion of the carburator body to do it's thing. The fast idle screw is above the other and acts upon a small flat portion of a part of the linkage attached to the carb. Both of these two screws face the left, normally driver's, side of the vehicle as I see them but I suppose that depending on their spatial position at a given time it could be said that they actually face the sky or the top corner of that wall over there, or even the door to the kitchen, but never the firewall.

Your Hayne's manual explains quite well the use and function of each of the relevant adjustments. The factory service manual does as well but with images that could be easier to understand. Perhaps it's time for you to go no farther until you are able to obtain a copy of that FSM for your vehicle?
 
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Jan 8, 2004
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hokay

The screw that I thought was for idle is behind the spring and metal lever towards the bottom of this picture. That screw pointing downwards at an angle to the left is sort of pointing at it. Anyway, when I turn this screw it adjusts idle, or appears to adjust idle. Is it "fast idle"?

This is on 78 2F. The carb in these pictures looks exactly like mine.



No where in this post did I refer to my truck as a car so I'm going to submit the post.
 

Pin_Head

 
 
 
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The screw in the base between the two throttle shafts is the main idle speed screw and it is not visible in the picture b/c it is behind the spring. The top screw you can see is the throttle positioner speed adjuster that regulates engine speed by the smog computer during dece3leration. The bottom screw is the fast idle associated with the choke.

HTH
 
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Nov 7, 2004
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Barrington, RI
Pin_Head said:
The screw in the base between the two throttle shafts is the main idle speed screw and it is not visible in the picture b/c it is behind the spring. The top screw you can see is the throttle positioner speed adjuster that regulates engine speed by the smog computer during dece3leration. The bottom screw is the fast idle associated with the choke.

HTH

I believe you can actually see the screw in the first picture but it's difficult because the screw head is painted the same color yellow as the background (camouflaged).
 
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