Q-Jet Adjustment
Thread Starter
Instructor
Joined: Oct 2008
Posts: 121
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From: Hooksett NH
Q-Jet Adjustment
When adjusting the idle mixture screws to achieve maximum vacuum, do you leave the settings at maximum vacuum, or do you then turn the screws back in a half turn to richen it up a little?
Advanced
Joined: May 2009
Posts: 65
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From: La Pine Oregon
Max vacuum should be no problem BUT turning those back IN would not richen ,
It would lean the mixture, THAT could be a driveability issue. It is best to err on the rich side if you are off on mix.
Bill J. (redstingray74)
It would lean the mixture, THAT could be a driveability issue. It is best to err on the rich side if you are off on mix.
Bill J. (redstingray74)
Melting Slicks
Joined: Jul 2006
Posts: 2,285
Likes: 487
From: Salmon Arm, BC
I went to the back end and listened to the exhaust for signs of a lean miss. Missing quite a bit so I richened 1/4 turn at a time until lean miss went away. Nice and crisp off idle now
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Thread Starter
Instructor
Joined: Oct 2008
Posts: 121
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From: Hooksett NH
I started with manifold vacuum hooked up to the vacuum gauge, both adjuster screws opened 3 1/2 turns (counterclockwise). At operating temperature and low idle speed, turn screws 1/4 -1/2 turn each until I got the highest vacuum reading going back and forth. I believe I got 15" with my cam.
Advanced
Joined: May 2009
Posts: 65
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From: La Pine Oregon
I have a 650 Holley vacuum secondary on a '74 L-82 350 w/4 Speed .
Here in central Oregon at La Pine the altitude is 4275 ft and my best vacuum is at
7/8 out from closed . The altitude really hurts vacuum and consequently power too.
Bill J. (redstingray74)
Here in central Oregon at La Pine the altitude is 4275 ft and my best vacuum is at
7/8 out from closed . The altitude really hurts vacuum and consequently power too.
Bill J. (redstingray74)
Advanced
Joined: May 2009
Posts: 65
Likes: 0
From: La Pine Oregon
Vacuum settings
Bill J. ( redstingray74) And you are very right about playing with Idle speed too .
Last edited by redstingray74; Jun 29, 2009 at 10:01 PM. Reason: Adding info I forgot.
Burning Brakes
Joined: Oct 2006
Posts: 1,089
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From: Native Californian CALIFORNIA
Army
I started with manifold vacuum hooked up to the vacuum gauge, both adjuster screws opened 3 1/2 turns (counterclockwise). At operating temperature and low idle speed, turn screws 1/4 -1/2 turn each until I got the highest vacuum reading going back and forth. I believe I got 15" with my cam.
By the way thanks for the advice as tuning by ear and feel is very difficult for me.
