Q-jet tunning fresh rebuild.

[Toronado]

Hello, I have heard many different opinions on how to adjust the idle mixture screws.
My 1970 Oldsmobile Toronado, needed a carb cleaning, so i rebuilt it.
Put it back on the car and started at 2.5 turns out. now the factory book
for my car says start with 6 turns out no joke six turns. Well the screws almost fall out
with six full turns. Currently it sounds good at 2.5. But i want to fine tune it.
I have heard the best way to tune a carb. by the idle screws is to listen as I turn the screws out
intell i reach the highest rpm the turn in a 1/4 turn in. Supposedly that is the best setting for performance, even though i have heard that you should turn them in as far as I can tell it sounds bad then turn them out 1/4 turn. My question is whats the best way to set them for street/strip stock car, these engines are already high performance at 375 hp and 510t. I figure it does not really matter since its only idle, and once I begin to depress the pedal the main jets take over no more idle circuit.
Thank you for any help

[omaha]

well. supposedly, the best way would be to use a vacuum gauge.  Try to get the highest vacuum reading at the rpm listed for the engine. (there's other ways to set this too)

[Toronado]

Ya you can run  tach to look for the right numbers,
not sure about a vac. gauge to tune the idle screws.
The pro,s say that you should listen for the highest rpms,
then turn them in 1/4, but this is not the leanest setting, according to others
opinions that I have heard. In other words you can set it for best idle performance,
or on the other hand you can set it for leanest setting while still maintaining an idle.
Two very different methods and styles, which ones the best-who knows.
I tend to think the leanest setting will not allow the car to launch well from dead stop idle to WOT!
You might even experience hesitation from small accel. pump shot and lean idle setting.
This is my third car with same carb. each car acts different depending on the mods.
My current car is stock, but is actually higher performance then my other 350 with headdars, high per. heads, msd, hei, cold air intake, elctric high per fuel pump, performance intake , cam ect.

[Cliff Ruggles]

If you don't have a vacuum gauge or tach, set the idle screws for the best idle at the leanest settings.

This is done by turning them in slowly until you hear or notice the engine slow down, then back about 1/2 to 3/4 turns. 

Balance each side as close as possible.

The idle mixtures screw setting(s) have NOTHING to do with WOT throttle response from or off idle. 

They can have an effect on transiton from idle to the main system at very slow/light throttle openings.  Even so, the size of the idle tubes, idle down channel restrictions, and lower idle airbleeds play a bigger role here.  Each carburetor should be set up exactly for the application, if you expect the best results.....Cliff

[Toronado]

Im curious why is it best to run idle at the leanest setting possible?
I was concerned about the transition you speak of,
from idle to main. My application all stock, I cruise around town mainly,
I dont race my car at race tracks, but I like the
response to be as fast as possible if I need to drop the pedal to the floor from dead stop.
Im still in the process of rebuilding this car, and tunning the car,
it set for a long time ran like crap when I got it runs great now, still have not
done a WOT test yet, still dialing it in.
Thank you for helping

[Schurkey]

Im curious why is it best to run idle at the leanest setting possible?

Not the leanest possible.   Find "best idle" (I use a vacuum gauge--about ten times more sensitive than a tach) and then go just a little lean.
Otherwise you're blowing incredible pollution out the tailpipe; and the excess gasoline will wash the oil off the cylinder walls and contaminate the oil.  From both the environmental and the engine-wear perspectives, overly-rich mixtures are detrimental.

[Cliff Ruggles]

Correct, not the leanest possible settings, but the best settings for the engine.  This is done by finding the lean "tip-in", then backing them out for highest vacuum, highest rpm, and best idle quality.

In most cases this will be about 1/2 to 1 turns from the lean "tip-in" point.

The idle system can certainly effect transistion, so it needs to be able to delivery adequate fuel thru the off idle transfer slots.

A "generous" idle system will not make up the main system being insufficient, so both items should be set up exactly for the application.

The quadrajet and Thermoquad are the best carburetors every designed for smooth idle/off idle and light throttle opening performance.  The small primary bores and booster arrangment is very efficient, and highly sensitive to throttle opening/vacuum changes.  With careful and correct tuning they will delivery perfect throttle response, and excellent economy.

Even so, non of these things have much effect going to full throttle, as the pressure above and below the throttle plates is equalized, and the accl pump, secondary POE, and main jets/secondary metering rod become the main players.....Cliff

[Toronado]

Thank you guys.....
I used the information you provided, now the car
has great response from stop to main fuel circuit.
Its very smooth & doesn't jerk forward in transition, even when the secondaries
open its a very smooth transition (like fuel injection) now the car has a very fast acceleration from stop to WOT without any lag through all the gears (constant pull).
Unlike some incorrectly matched carbs and engine combos, its not snappy off
the line then lags, then will jerk
forward when secondaries open then lags, no smooth power band. Just goes to
shows a rebuild isn't much without tuning it correctly.
Now my car is "SCARY" fast.

[Schurkey]

Now my car is "SCARY" fast.

When you're ready to start work on the suspension of that Toronado, so it isn't so scary...let me know.  I can help.