carburator

[tdag]

at the moment i am rebuilding a rochester 4 barrel on my 85 camaro. what i need to is what are the specks for setting the lean mixture screw. thank u

[NailZ69]

All engines require an acceptable air/fuel ratio to run properly, even at idle. Stock or mildly tweaked engines generally idle at 16-18 inches of intake-manifold vacuum between 750 and 900 rpm. Carburetors equipped with adjustable mixture screws allow the tuner to change the amount of fuel delivered to the engine, creating an ideal idle mixture.

On most carburetors, turning the idle mixture screw clockwise leans the idle mixture. Turning the screws counterclockwise richens the mixture. If there’s a vacuum leak, it must be repaired before the idle mixture can be properly adjusted.

All stock engines specify a certain idle speed, but generally 800-850 rpm works well. Properly setting the idle mixture also creates the highest manifold vacuum, so a vacuum gauge makes the task easier.

The best backyard procedure for setting idle mixture is the idle-speed-drop method. First, connect the vacuum gauge to the manifold. Adjust the idle mixture richer or leaner until the highest vacuum is read. Once that’s attained, turn the idle mixture screws leaner until the rpm begins to drop, then turn the screws richer a slight amount. The ideal idle mixture has now been set.


If you don’t have a vacuum gauge, use a low-speed tachometer. The tach should have a low-scale readout that’s sensitive to increments of at least 50 rpm. Use the tach to help you adjust the idle-mixture screws evenly to create the highest idle speed. If the idle speed exceeds 950 rpm, use the idle speed screw to slow down the engine, then readjust the idle mixture.

[NailZ69]

come back if u still have problems

[NailZ69]

To tune the engine for maximum power. Turn the mixture screw in (clockwise) 1/16 of a turn and continue driving. Note any increase in speed and performance. Continue to lean the fuel mixture in 1/16 turn increments until :

1) There is no longer any performance increase or
2) The engine begins to cut out at high speed or
3) The engine begins to overheat

If you are using a digital temperature gauge, the Pro .15 tuned for performance runs in the range of 300° to 320° F.