Instructions

1. • 1

     Needle VALVESMake sure your vehicle transmission selector sits in park or neutral, depending upon the type. Apply the emergency brake. Raise the hood and disconnect the negative battery cable with a socket and wrench. Remove the air cleaner housing by unscrewing the top lid bolt and frame brackets with a socket and wrench. Twist off the butterfly nut on the lid by hand, if so equipped. Refer to your owner's manual for the location of your idle mixture screws on the base of the carburetor.

   • 2

     Look for a round-head screw encased in a spring protruding from the carburetor base. Hook one end of a tachometer lead to a bare-metal ground source on the engine. Hook the other tachometer lead to the negative (-) side on the ignition coil terminal. Temporarily connect the negative battery cable by hand and start the engine. Let it warm up to normal operating temperature, or until the choke valve opens on the carburetor.

   • 3

     Note the reading on the rpm on the gauge. For instance, it might read 700 rpm. Place a slot-head screwdriver on the mixture screw and begin to turn it clockwise. Note the rpm change on the tachometer. If you do not see a noticeable drop, or any drop on the gauge, even when you turn the screw all the way into the seat, the needle valve has failed to seat properly. Shut off the engine and and disconnect the negative battery cable.

   • 4

     Use the screwdriver to turn the mixture screw counterclockwise all the way out of its seat. Pull the spring off the needle valve. Examine the needle valve tip -- it should be tapered, clean and shiny. If the tip end appears crushed or the rod appears bent or grooved, it must be replaced. If the tip end has carbon and sludge on it, spray it with carburetor cleaner and gently wipe it clean until no debris remains on the end.

   • 5

     Look inside the carburetor seat and pull out the small ring gasket. If the gasket looks crushed, cracked or deformed in any way, replace it. Use the high pressure nozzle on the spray cleaner can to blast the inside of the seat area, removing all carbon and sludge. Pull on the spring ends to lengthen the spring, but don't overdo it. Put the spring back on the needle valve and screw it into its seat. Do not over-tighten it.

   • 6

     Turn the mixture screw counterclockwise 1 1/2 turns out for an initial adjustment. Reconnect the negative cable with a socket and wrench. Start the vehicle. Let it warm up. With the gauge still attached, note the rpm reading. Adjust the screw by turning it slowly clockwise. If the engine begins to falter and you see a drop in rpm, you have successfully tested and repaired the needle valve. Adjust the screw, by turning it in or out to achieve the highest rpm on the gauge.

   • 7

     Use your repair manual to locate the idle speed screw on the carburetor linkage. Adjust your idle speed, by turning it in or out until you achieve the manufacture's recommended idle speed. Unhook the gauge and replace the air cleaner housing and brackets. Tighten the bolts with a socket.