There should be two screws on your throttle arm. One screw makes contact with with the carb's body, that is the hot idle speed adjusting screw. You adjust the motor RPM with that screw after the motor is up to operating temp and the choke plate is wide open.

The second screw seats against a plastic cam piece that moves with the choke plate by means of a rod linkage. That plastic cam piece has 3 steps on the that the screw can sit against. To set that screw for proper position, With the motor not running, you will need to open the throttle about 1/2 way open, and manually close the choke plate. The closed choke plate should lift the linkage up and lift up the plastic cam piece so when the throttle is released, the screw sits against the highest step that the screw can contact (but you need to be sure the throttle was open far enough for the linkage to lift the plastic cam all the way up without the screw touching the cam before the throttle is released). The information on the carb rebuild kit will give you the proper way to set that screw for the "fast idle". Things have changed enough through the years, you need to set "the fast idle speed" the way the info instructs you to set it.

There is one more important note here. While setting the fast idle speed, there is also a vacuum diaphragm called "the choke pull off" that needs to be tested. The diaphragm has a rod linkage the connects to the choke linkage. There is also a vacuum hose connected to the diaphragm that also connects to a vacuum port on the bottom throttle body. The vacuum hose needs to be soft, pliable, and without cracks or it needs to be replaced before the test can be done. You need to disconnect that vacuum hose at the carb base, and push the plunger on the diaphragm in all the way, then while its pushed in, cover the end of the hose with your finger to seal the hose. When you release the plunger, the plunger should stay sucked in until you release your finger from the hose end. If the plunger does not remain sucked in, either the hose or the choke pull off plunger is defective. Replace either (or both) of the defective parts. If the plunger remains sucked in until you remove your finger covering the vacuum hose, the choke pull off and the vacuum hose are good
The purpose of the choke pull off is to open the choke plate enough for the carb to get enough air when the motor is cold and the choke is in operation, so the motor can run. If the choke pull off and the hose are good, the next thing that needs to be checked is how much the choke pull off linkage is opening the choke plate. This test needs to be done with the plunger fully pushed in on the pull off diaphragm. You either need a vacuum pump to keep the plunger in, or you can push it in manually, and use something to temporarily plug the end of the hose. You will need both hands to check the gap between the choke housing and the choke plate. That gap is normally checked with a drill bit of a specific size (the instruction do lay out the process and the drill size).

The process is: Motor not running and choke rod from the intake disconnected. With the fast idle set screw positioned on the highest step on the plastic cam, and the throttle in the closed position against that screw, you insert the correct size drill bit along the inside of the carb body, and apply slight pressure to close the choke plate. The drill bit should slide in and out between the carb body and the choke plate with a slight drag. The little rod between the diaphragm and the choke linkage is either bent together at the U bend for more opening, or spread farther apart at the U bend to close the plate more. A slight bend can make a huge difference in the amount the choke plate opens and closes with this adjustment. After the adjustment is complete, reconnect the vacuum hose to the carb base, and reconnect the choke rod from the intake.


As a program note, after a few engine cycles (warm up and cool down, if there is a slight stumble leaving a stop, while the motor is cold and the choke is closed, a slight closing of the choke pull off rod may improve the cold engine operation, if the motor seems to run pretty rich while the motor is cold and the choke is closed, a slight opening of the the choke pull off rod can improve the cold motor operation. These adjustments won't make any difference once the motor has warmed up and the choke is no longer in operation. If the motor is warmed up (read that at or very near operating temp) and the choke is still under pressure to close, either the choke spring pressure needs adjusting, or the intake crossover the choke uses to function is plugged up.

Another program note, most chokes do not function well until the outside temp gets below 50 degrees. They were designed to function in colder weather. Gene