467-Ratman

I checked out the 4 idle screws on my carb and the way its set right now all four are 3\4 of a turn out. I attempted to adjust the back set in but when I turned the pass side screw in the motor really slowed down. As soon as I turned it back to 3\4 its fine. The motor seems to be rich at idle thats why I was attempting the change. Can someone explain again the basics of adjusting the idle screws? :confused:

69 N.O.X. RATT

Screwing the idle screw clockwise (in) cuts the amount of fuel, basically leaning the mixture out.

If your car will idle decent the way to do it is to start with all four 1 -1/2 turns out from bottomed out, then SLOWLY turn the screw either clockwise or counter and look for a gain or drop in rpm. If you gian some rpm then adjust your idle back down to where you want it and start over again on the next idle adjustment screw. When you get max rpms out of the screw you are done, go to the next.

1979toy

You've got a lot of camshaft there. Try opening the throttle blades a bit then start over on the idle mixture screws.
In the old days we used to have to drill holes in the throttle blades to do the same thing.

Brettmc

The way I did it was to buy a vacuum gauge ($25 at AutoZone) and adjust the idle mixture for max vacuum. The same vacuum gauge can be used to determine if the power valve in your 850 is right for your motor.

How much of the transition slots are exposed?

Oh yeah, when you adjust the idle mixture, try turning the screws just a little bit, like 1/8 of a turn at a time.

Brett :thumbs:


[Modified by Brettmc, 5:21 PM 7/5/2003]


[Modified by Brettmc, 5:22 PM 7/5/2003]

bence13_33

The first thing you need to check is how much of your transition slots are exposed? There should only be a very small bit of the transition slot exposed. If you have too much of the transition slot exposed it throws the whole idle circuit out of whack.

With the cam you are running you should not need to drill holes in the primary throttle plates. This is a last resort to try to get a very large cammed motor to idle correctly. A lot of people do this without even taking into consideration the secondary throttle plates. There is a set screw for the secondary throttle plates. You can open them up more to allow more air at idle. Your primary and secondary throttle plates should be opened almost the same amount. In other words the primary transition slots should be showing almost the same as the secondary transition slots.

As for the position of the idle circuit screws, it will be different from motor to motor. However a widely accepted setting is 1 1/2 turns from the bottomed out position. But don't be surprised if your setting is only 3/4 of a turn. The easiest way to set the idle circuit screws is to bottom the screw out and SLOWLY turn it counter-clockwise. The reason you slowly adjust it is because the idle circuit is slow to react to any changes. Keep turning it counter-clockwise until you hear the idle start to drop. Once you hear the idle start to drop give the idle circuit screw an 1/8 of a turn clockwise.

I love driving my car ever since I leaned it out. I always used to foul plugs driving around town. My gas mileage is much better than it used to be and so is my performance. The best part of it all is I can let it idle in the garage and it won't burn my eyes anymore.

norvalwilhelm

Good advice Shane.
You can also lean out the idle circuit by taking pieces of about .015 copper wire about 3/4 inch long and bend them in little "L" s. Put them in the idle circuit meetering plate and the gasket covers them to keep them from falling out. This leans out the idle mixture, is also recommended by holley to increase the sensitivity of the idle screws and allows you to get closer to the recommended 1 1/2 turns out.
I have these wires in both my 850 carbs idling circuits. Drilling the throttle plates and installing these little wires are a normal modification for me.

LAvetteman

On my old Holley 750 the screws were set at about 1 1/2 turn. On my Demon 850 the screws are at 3/4 max.