Priya

I noticed the exhaust at idle on my 79 L82 was making my eyes burn and was sure the idle mixture was too rich. I started by turning the screws all the way in, they were 2 & 1/4 turns out. I turned them out 2 turns and started turning them in from there looking for a rise in vaccuum readings - the readings dropped. I ended up getting maximum vaccuum at 3 & 3/4 turns out, the exhaust is still burning my eyes and it doesn't idle any smoother than it did. 3 & 3/4 turns seems like much more than it should be to me, is there something else wrong, or is this to be expected sometimes?

Stock motor and quadrajet carburetor.

Haggisbash

There is something wrong, have you checked the choke is working properly?

Priya

The choke was wide open when I was doing this. On a cold motor I pump it twice, the choke closes fully, it fires,runs rough and slow, I step into the gas, the motor chugs and revs like too much gas, smooths out,goes to fast idle, idle drops off but runs smooth,step into gas for 30 seconds or so and then it runs on fast idle and runs nicely after that and warms up normally.

DUB

have you turned the idle mixture screws IN until they either bottom out and stop or the engine dies????

YOU are doing this with the air cleaner ON...CORRECT???

Is your ignition system in very good condition...and are you sure your timing is where it needs to be???

QUESTION: Why did you choose to turn the idle screws in the first place...just curious?

DUB

Priya

I have turned the idle mixture screws all the way in until they bottomed and did that each time I tried a new setting just to be sure. the screws have been bottomed each time and tried at 1 turn, 1 &1/2 turns, 2 turns, 2 & 1/2 turns, 3 turns, 3 & 1/2 turns, and 3 & 3/4 turns which gives the highest vaccuum reading.

The spark plugs were changed last year, just replaced the plug wires, distributor cap and rotor and centrifugal advance mechanism. I checked timing yesterday, its set at 12 BTDC

I am doing this with the air cleaner OFF, but I have the vaccum gauge plugged into the vaccum port on the carb where the air cleaner vaccum line went. I can't reach the idle mixture screws with the air cleaner on.

I wanted to adjust the idle mixture screws because the idle is rougher than I think it should be, the exhaust was burning my eyes, the carburetor has been rebuilt and the ignition system thoroughly gone over - idle mixture screws seemed like the likely culprit.

gcusmano74

Check with Lars to be sure, but I don't think that 3 turns and a bit more is excessive. I believe your problem could be elsewhere.
The factory used very small idle fuel orifices to make sure the idle never got too rich. A smaller fuel orifice also gives you a nice fine adjustment of the flow, as well.
I (unfortunately) once had a Qjet "professionally" rebuilt. They opened up the idle orifices so big that the difference between WAY too rich and WAY too lean happened within only an 1/8 turn of the screw, total turns open was about 1 1/4. It was #$%^ near impossible to get a decent idle.

Priya

I wouldn't be concerned about it if the idle had improved and the exhaust weren't still burning my eyes and smelling rich. That's what I don't get, no matter how much I turned the screws in the exhaust never stopped smelling rich.

Haggisbash

Okay, so when you bottomed out the idle screws did the motor die? If it didn't its picking up fuel from another circuit so the problem is unlikely to be the idle mixture screws JMPO. Sorry I'm not too sure what to look at on a Qjet as my car came with a Holley. Have you checked the fuel level in the fuel bowl?

Priya

I have not checked the fuel level in the fuel bowl. When I was resetting the idle mixture screws to 1 & 1/2 or 1 turn out I was turning up the idle speed so the motor didn't die but the idle speed had dropped with the fewer turns open. I never closed the idle mixture screws all the way while the motor was running. I turned off the motor each time I bottomed them out before I opened them up again however many turns.

Haggisbash

Wont hurt to try bottoming the screws with the engine running, it should stop when you do. Did the engine always smell rich like it is now? If it didn't we need to establish what has changed.
I see you are twiddling the ignition timing as well? My suggestion would be to get that finished before returning to the carb. A wise forum member remarked that 90% of carb problems turned out to be ignition ones. I understand that a QJet can be set up to meter fuel very accurately so there is no reason it should be running rich once properly set up.

Priya

I'm confident I've got the timing well sorted out. The exhaust burned my eyes and smelled rich at every idle mixture screw setting I tried. The idle might have been slightly rougher at 1 & 1/2 turns out and 1 turn out but for the most part the idle was the same at all settings.

I'll try bottoming out the screws with the engine running tomorrow and see if it dies.

Haggisbash

Okay, so I'm pretty sure that the engine is getting extra fuel from somewhere other than the idle circuit. So, if the choke circuit is not the culprit I would be checking the fuel level in the fuel bowl as in most carbs if this is too high the mixture can be too rich. Its about now we need a QJet guru!

Haggisbash

Could be as simple as the float not closing properly because or a bit of crud under the float valve holding it off its seat.

Priya

Sounds plausible, I'll check into that as well tomorrow - thanks.

Shark Racer

What was the highest vacuum reading you got?

Did you check for nozzle drip? This is when fuel drips out of the nozzles like a sink that was just barely left on. I put a flashlight into the bores and check for it. I usually check across the engine (from driver's side to passenger side venturi, vice versa) to avoid sticking my face above the carburetor in case of backfire. You can also use a mirror or a camera for safety.

Make sure to re-adjust your idle RPM as re-setting the mixture can change it.

The motor should also be completely warmed up when you set the idle mixture.

Garys 68

What does this mean?
"I have the vaccum gauge plugged into the vaccum port on the carb where the air cleaner vaccum line went."?
And how do you plan on checking fuel level in the bowl?

71scgc

Send an email to Lars at:

v8fastcars@msn.com

P.S. Check your "all in" timing.

Carter

Priya

The highest vaccuum reading I got was a little over 15 in, the lowest was about 13 in.

I never heard of nozzel drip so I didn't check it. Not sure what a nozzel is, are you referring to the little circular things that are in the middle of the venturi that vaccuum sucks gas out of?

The motor was fully warm when I adjusted the mixture screws and I reset idle speed each time I adjusted them.

Priya

There's a vaccuum port on the back of the carb's lower base that a vaccuum hose from the air cleaner goes on. To remove the air cleaner you have to remove this hose. To avoid a vaccuum leak I hooked the vaccuum gauge to that vacccuum port after I removed the air cleaner.

I figured I'd take the top of the carb off and hold a lighter above it to see how much fuel is in there.

Priya

Thanks for the email Carter, I'll send lars an email and see if he'll comment.

I have checked my all in timing and its about 28 degrees at what I guess is 4000 rpm ( I was by myself so couldn't read the tach).