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1979 Truck 20R carb tuning help?

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Old 07-16-2011, 01:46 PM
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1979 Truck 20R carb tuning help?

I have looked but cannot find the factory specs for the idle air mixture screw, I know it is running rich, but how much I do not know. It was 5 turns out from closed.
Old 07-17-2011, 09:55 AM
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Is there a way to tune it?
Old 07-23-2011, 09:14 PM
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bring it to a shop and get a tune up, sounds like you wouldn't know where to start lol
Old 02-05-2012, 05:34 PM
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Truck is tuned up. new plugs, wires, cap rotor, air filter fuel filter... everything that I can think of that can affect tuning... I was getting around 15mpg, now about 12mpg. Driving is 60 highway/40city, driven aggressively for the little truck. Nothing rebuilt... any specs? I cannot find them anywhere.
Old 02-09-2012, 10:08 PM
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lean it out until it idles highest, then make it a little richer
Old 02-10-2012, 05:49 AM
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Usually, turn the idle mixture screw in until it just bottoms out, the unscrew about 2 1/2 to 3 1/2 turns. Start engine and set the idle speed to around 750-800 rpm. Adjust the mixture screw in/out 1/2 turn to get smooth idle. I usually bump the throttle after each adjustment checking for smooth acceleration off idle.

You can download the FSM here http://www.ncttora.com/fsm/ Scroll down to the 79-85 section. There's a lot of info in this PDF file. Carb adjust is in the fuel section

Last edited by Lons81; 02-10-2012 at 06:22 AM.
Old 02-10-2012, 10:11 AM
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Originally Posted by Yota1979
bring it to a shop and get a tune up, sounds like you wouldn't know where to start lol
That is not very nice we are a helpful community my man
Originally Posted by the big d
I have looked but cannot find the factory specs for the idle air mixture screw, I know it is running rich, but how much I do not know. It was 5 turns out from closed.
Would this be a stock carb or a weber carb or asia carb?
Old 02-10-2012, 12:11 PM
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The factory carb btw.
Old 02-10-2012, 12:35 PM
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5 turns out sounds extremly rich, any mods? i expect your plugs were looking black, most carbs, you will bottom out the air mixture screw(s) then start at 1 1/2 turns out, if doing by ear, i would do what was mentioned above by lons81. jmo
Old 02-10-2012, 03:41 PM
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Stock engine, 360k or 460k miles. (Uncle can't remember how many times it rolled over)
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