Carburetor Tuning Instructions

These instructions are intended for someone who is experienced in automotive repair and repair safety. Working on any fuel system requires that the engine be cold and to have a fire extinguisher present at all times. The work area must be kept extremely clean as if dirt enters the jet system it will seriously affect the operation of the fuel metering system. Clean all fuel spills immediately to eliminate the chance of a fire.

1. Start the engine and bring it up to full operating temperature, if the vehicle is drivable the best way to bring the engine to full operating temperature is to drive it for 20 to 30 minutes.


2. Remove the air filter assembly and start the engine, disconnect the throttle linkages to the carburetors.


3. Using the STE carburetor synchrometer locate the highest flowing barrel on each carburetor.


4. Balance the carburetors from side to side first, using the highest flowing barrels on each side, adjust the carburetors by turning the idle speed screw located on the front of the carburetor, the engine should start to smooth out if the carburetors are out of balance.


5. Next on carburetors that have balance adjustments between barrels, (Solex split shaft and Weber carburetors), adjust so that each barrel is flowing the same amount of air flow. After balancing all barrels re-check the side to side balance and re-adjust if necessary. (Note: The Solex split shaft carburetor is adjusted by turning the throttle balance screw located in between the barrels. Weber carburetors are balanced by turning the air bypass screw out located just above the idle mixture screw. As a side note before balancing Weber carburetors loosen the lock nut for the air bypass screw and turn all bypass screws in until they seat against the carburetor body. When balancing air flows only adjust those cylinders that are low flowing.)
   
   
   Mixture Adjustment
   
   


6. After the air flow has been balanced slowly turn each mixture screw in until you can hear a change in the note and speed of the engine, (Be careful not to bottom the mixture screw out too hard as you can damage the mixture screw and or the carburetor body.) If the engine speed increased, keep turning the mixture screw in until the idle speed drops then turn the screw out until the engine speed increase’s again.


7. Move on to the next cylinder and repeat step six until all cylinders have been adjusted, you may have to adjust the idle speed lower after you complete the mixture adjustment on all cylinders. Remember to adjust each idle speed screw equally and re-check the balance using the STE balancer.


8. It may take two or three times over each cylinder to get the engine idling smoothly and at the correct speed. If a mixture screw does not change the engine speed when it is screwed all the way in, then there is a problem with that cylinder. Stop the engine and pull the plug to see if it is wet/fouled, check the compression and leak down on that cylinder if you haven’t already done so, Check the plug wire and spark plug connector. If the fuel system is dirty you may have debris in the idle control system, if so remove the mixture screw and using compressed blow through the circuit and then re-try to adjust thecarburetors