1956 Corvette: Service Bulletin: Spark Plug Fouling - Idle Adjustment
Subject: Spark Plug Fouling - Idle Adjustment
Model and Year: 1956 Corvette - Dual 4-Barrel - Carter Carburetor
Source: Chevrolet Technical Service Bulletin
Bulletin No: DR #258
Date: August 30, 1956
TO: ALL CHEVROLET DEALERS
In cases where Spark Plugs are wet fouling on V-8 Engines used in 1956 Corvettes with dual 4-barrel carburetors being operated in Metropolitan Areas which put considerable limitation on their top speed, it may be necessary to install AC-46 Plugs to correct this condition.
AC-44 Plugs are to be furnished in production.
Range of plug should be tailored to the owner's requirements:
AC-44 Extreme High Speed Driving
AC-44 Medium High Speed Driving
AC-45 City Driving and Normal Operation
AC-46 Metropolitan City Driving Under Heavy Traffic Conditions
IDLE ADJUSTMENT - CARTER DUAL 4-BARREL
To obtain a consistent idle speed setting on V-8 Engines equipped with Carter 4-Barrel Carburetors with regular or racing camshaft, proceed as follows:
Engine Number Suffix -
GH Regular Camshaft
GU Racing Camshaft
- Set bypass idle screw on each carburetor 1-1/2 to 2 turns open. (Located on left rear corner of throttle body).
- Set both idle mixture screws on each carburetor one turn open.
- Obtain from Parts Stock and install throttle valve set screw #566247, spring #1451460, and washer #566255 on rear carburetor in threaded hole provided.
- Start engine and set throttle valve set screw for 600 RPM (regular camshaft) or 800-850 RPM (racing camshaft) as required.
- Adjust all idle mixture screws individually for best engine RPM.
- Reset throttle valve set screw to original RPM setting (600 or 800-850 RPM).
- Again adjust all idle mixture screws individually for best engine RPM.
- Reset throttle valve set screw to 600 or 800-850 RPM.
- Bypass idle screws on each carburetor need not be adjusted after initial setting in Step #1.