How to set the mixture in a Q-jet.

[Disturbed Berlinetta]

How to set your mixture on a Q-jet carb

1st , there a special instrument that is designed to read mixture on an electronic carburetor, I am not sure what it is called but it is made by Snap-On tools or craftsmen, ask for what the tool does and they will know what it is, or ask a mechanic.

2nd the idle screws are on the left and right corners of the primaries, you won’t be able to see them, because they are covered by rubber caps pull out the caps.

3rd the lead going to the solenoid, there are two wires there are probe leads that comes with the kit, attach the colored clamp from the meter to the side of the plug you want to check if it is the left lead then it is the left screw, also ground the black lead, now on the meter should have a scale from 0-60, 0 being way lean 60 being way rich, so lets say if the right lead reads 10 on the meter you would, move the right mixture screw out to richen it until the meter reads 30, that is a “perfect mixture” repeat the same with the left side lead and screw.

And that is how you adjust the mixture on a Q-Jet carb.

[ultimate-second-gen]

I think you be better off getting a real carb like a Holley. My second gen has a REAL carb and a REAL motor. http://www.3rdgen.org/ubb/tongue.gif LG4 is trash. 150hp POS

[BEER]

Yea! get a 200 hp piece of shit that's ugly

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Clean 85 Z28 w/TPI, rare black contour interior( 1 of 2,510), almost every option except for a posi rear, go figure.
79 malibu demolition derby car (still have movies to post)
87 parts car, which previously was a high 13 second Lg4 car (broken frame and all twisted up)

[Disturbed Berlinetta]

ok first no shit the Q-jet is a pos but I was writing that artical for those who still want to have and do still have a Q-jet

.....so kiss my ass

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If it doesn't have an eight I won't Drive it. http://jcauto.simplenet.com/pee.gif http://jcauto.simplenet.com/Hbadge.jpg

[84FBODY]

There's nothing wrong with the Q-jet. It's a good carb and can flow over 800 CFM. Not that difficult. Sheesh. As far as LG4's go They're good engines and can be just as strong as a 350 (With more money of course) They go a long time. Mine in my 84 went until spring of 2000 16 years is pretty good for a "piece of trash".

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John- 1984 camaro, 350, Dynomax Cat-back, busted tranny.

Warrior Court Jester of the Not So Famous Cascade Crew.

http://www.vision2100.com/mt3.jpg

http://www.suempresaenlinea.com/drowned/images/iroc-gray.gif http://www.suempresaenlinea.com/drowned/images/iroc-front-gray.gif

If you can read this MY TRANSMISSION IS STILL BROKEN!

[Newsance]

Here is what you need to do to set mixture on a feedback (electronic quadrajet) carb.

1. To set idle mixture, you need to drill out two tabs on the bottom of the carb. With the carb off of the car, it is easily seen where this is. The tabs block access to the idle mixture screws. There is one screw for each side of the carb. When you back out the screws, the idle mix gets richer.

How to adjust, is with the carb running, back out the mix screws SLOWLY, unil the engine is running at it's peak rpm at idle. Then move the screws in until it the idle just begins to get rough again, then back them out from that point 1/4 turn.

2. To adjust the main metering mixture, it is a little bit tougher, but can be done. First what you need to do is connect a dwell meter to the Mixture Control Solenoid. The MCS is the left plug on the top of the carb as you look at it from the front of the engine.

What the MCS does is regulate the air/fuel mixture electronically during part throttle. This is the computerized part.

To connect a dwell meter, Look for a connector that is not connected to anything in the wiring harness next to the carb. It will have 1 wire, and in mine it had a green connector. You will connect the dwell lead to this.

With the dwell meter, set it to 6 cylinders . Why? Because you are measuring the time that the solenoid is energized, and the 6 cylinder scale gives you numbers that can easily be converted to percentages.

With the dwell connected, start the car and run with it warm. Make sure that it is in closed loop mode, where the computer is changing the fuel mixture based on O2 sensor readings. You can verify this by making sure the needle is jumping around on the dwell meter when the engine is at the same rpm.

First, ensure that the computer system is operating properly. Drive the car around and watch the meter. Under hard acceleration, is should move to the right, but it should vary. What you need to ensure is that the needle is not staying far to the left, of far to the right.

If it is, this means that there are other problems. If the needle is to the left, teh computer is seeing a continuing rich signal at the O2 sensor, so is adding the minimum amount of gas to the system. This could be caused by a bad airfilter, a dead cylinder, or a carb that is leaking unmetered gas into the engine.

Far to the right means the computer thinks the engine is running too lean based on the o2 sensor, and is adding much more fuel to compensate. This lean condition could be caused by a vacuum leak or similar condition.

With this checked, now is time to TUNE! To do this on the car, you do need a special tool from snap on. This tool fits into a hole on the air horn, and allows you to adjust the amount of travel the MCS has. More travel means that it will allow in more fuel when it cycles on, less travel means less fuel. This way you can modify it to provide more juice for a lerger motor, while still not having the MCS maxed out (being on all the time).

What you do is simply back the MCS adjusting screw out a 1/2 turn at a time, then drive and watch the dwell. The dwell reading should decrease with the more travel the mcs has. It is also a good idea to COUNT the amount of turns you have moved the screw from the baseline setting, so you can set it back if need be.

Thats it! tell me if you have any questions. These can be good street carbs, the only real downside to them is they don't work well on larger engines as the fuel well is too small and gets drained quickly at WOT.

[Disturbed Berlinetta]

Thank you that is what I was trying to explain.

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If it doesn't have an eight I won't Drive it. http://jcauto.simplenet.com/pee.gif http://jcauto.simplenet.com/Hbadge.jpg