Quadrajet Adjustment

drsantos · 03-18-03, 11:10 AM

WHAT IS A GOOD STARTING POINT (#OF TURNS FROM BOTTOM) TO SET THE LEAN MIXTURE ADJUSTMENT SCREW ON A 1981 Q-JET?

68Roadster · 03-18-03, 08:54 PM

A reading from the book of Rochester......

Turn mixture screws clockwise until they are lightly seated
Then turn counter clockwise about 2.5 to 3 turns
This provides a preliminary idle mixture adjustment

Idle adjustment - engine running
Turn each idle screw clockwise until the idle drops a noticeable amount then.....
Slowly turn the mixture screw counter clockwise until the maximum rpm is achieved, but no further.
Work from one screw to the other, making sure both screws are about the same number of turns out. This assures mixture balance.

Check idle to speed to ensure still correct

Happy Tweaking!

1969D_Floyd · 03-19-03, 12:33 PM

The recent 70 degree temps in Chicagoland brought my '69 out of hibernation over the weekend. One problem did occur - the engine lost significant RPMs while accelerating between 50-60 MPH. It has happened before. I wonder if the Q-Jet needs adjustment. It seems like I flooded the engine. Does this sound like a simple tweak would help?

68Roadster · 03-19-03, 01:53 PM

Is it missing under acceleration?? If so I would check the points and cap first......unlike the new cars, sometimes we have to re-adjust the points and dwell after 1000/1500 miles or so.....

Have fun....enjoy the sun!

Enigma · 03-19-03, 07:07 PM

Another method I used was to hook up a vacuum gauge.

Then from the point 68Roadster has U at , adjust until there is max vacuum reading.

Worked for me.

Enigma

Stingray6974 · 03-19-03, 09:57 PM

I hate to be the bearer of bad news. All the suggestions are good but they will not work on an '81 carb. This carb is computer controlled. As you try to richen the mixture the comp will attempt to lean the mixture and vise-versa. The idle mixture must be set with a dwell meter or scanner.

Mike

68Roadster · 03-19-03, 11:31 PM

That the sounds Mike's post made when I opened it up......

See what happens when us rookies get involved.....I think I'll stick to posting in the Humor Mill forum......at least there I can't do any harm.

Thanks for enlightening me Mike.....again......

mmvette80 · 03-20-03, 08:05 AM

Just last week I messed with the screws. I turned them counter clock to seat them and backed them off clockwise to 2 turns. The car runs better and dont smell rich. Is this possible? Is the carb getting too much fuel? Also when I backed them off counter clockwise the car stalled. My carb is the original from 1980.

Bob Chadwick · 03-20-03, 08:10 AM

Quote:

Originally posted by mmvette80
Just last week I messed with the screws. I turned them counter clock to seat them and backed them off clockwise to 2 turns. The car runs better and dont smell rich. Is this possible? Is the carb getting too much fuel? Also when I backed them off counter clockwise the car stalled. My carb is the original from 1980.

You should expect some negative impact on idle as you adjust the idle mixture screws. When you get the best idle, or if using a vacuum gauge the best vacuum, the idle mixture is supposed to be properly set.

mmvette80 · 03-20-03, 08:19 AM

OK. Ill let the car warm up. Then hook up the vacuum gauge. Then back the idle mixture screw clockwise to seat and then back off 3 turns to start. Then fix the idle (rpms). Then adjust to get the most vacuum?

Bob Chadwick · 03-20-03, 09:54 AM

That's how I did mine, only I didn't use a vacuum gauge. I just listened for the smoothest idle.

mvftw · 03-20-03, 10:57 AM

I also did mine awhile ago the bobchad method and work well.

drsantos · 03-21-03, 04:29 PM

Thanks for the info, but the setting I am looking for is internal to the carb it adjusts the stop idle solnoid. it is part of the piddle valve plate of the mixture control solenoid.

68Roadster · 03-21-03, 04:35 PM

I have a Rochester book but I need to know the carb model.
Maybe the answer is in there.....

Look when I get home......

Stingray6974 · 03-21-03, 10:57 PM

There are three adjusters for the m/c solenoid. Which one are you trying to adjust? The solenoid height, the metering rod stop, or the idle air valve?

Mike