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Setting Carburetor Air Fuel Mixture
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Step 1: Get the vehicle up to operating temperature.
Do not set the mixture if the vehicle is cold, if needed do step 5
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Step 2: With the vehicle off turn the mixture screws all the way in.
Dont tighten them a lot though, you could do damage
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Step 3: Back both mixture screws out 1-1/2 turns.
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Step 4: Have your vacuum gauge hooked to full manifold vacuum.
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Step 5: Start the truck and set the desired idle speed (700-800 rpm)
If the truck will not run try backing out the mixture screws another 1/2 to 1 turn
This is also a good time to check the timing, a timing light with tachometer is helpful.
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Step 6: Back out the right mixture screw 1/4 turn, then back out the left mixture screw 1/4 turn (keep them even)
The vacuum should rise
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Step 7: Reset your desired idle speed
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Continue steps 6 & 7 until you reach the highest vacuum (a good range is 18-22)
You will get to a point were the vacuum stops rising.
Once you turn the mixture screws 1/4 turn and there is no vacuum change you know you are at the highest vacuum setting.
Turn the mixture screws back the 1/4 turn to were they were the highest.
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Notes to remember:
Always keep the mixture screws even, if you turn 1 screw a 1/4 turn, turn the other screw 1/4 turn.
Adjust your mixture screws in small adjustments, 1/8 or 1/4 turns, 1/2 turns and full turns are not recommended.
Keep setting your idle speed after every mixture screw adjustment and check you vacuum gauge reading.
Once you have the highest vacuum and desired idle speed your are ready to go.
For emissions you may want to turn the mixture screws back in another 1/8 to 1/4 turn.
I have used this method a few times now and it has always worked great and I have passed emissions with no problem.
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