Quote Originally Posted by duskylim View Post
Dear Sir:

900 to 1000 rpm is around normal for a 12R at FAST IDLE - when the A/C is ON.

When the A/C is OFF the idle speed should be around 700 to 800 rpm. That will help a lot with fuel economy AND make it easier for you to shift in traffic.

Your carburetor should have an FAST IDLE system - this is usually a solenoid-switched, vacuum-actuated diaphragm that pulls the throttle to a higher setting (higher rpm) for powering accessory loads like the air conditioner.

Note: this system is different from the one you previously adjusted the CURB IDLE with. It has it's own adjustment screw.

To look for the system, first set your curb idle to 700 to 800 rpm - like you did before. The CURB IDLE screw is always very close to the carburetor body and farther away from the throttle linkage.

Then with the air cleaner assembly removed, and the carburetor throttle linkage exposed to your view, have someone inside the car turn on the air conditioner.

You should notice the 'click' of the solenoid and some movement around the carburetor's throttle linkage system.

Look for a vacuum diaphragm that pulls the throttle shaft to a higher setting - you can't miss it if you know what you are looking for.

That's the FAST IDLE SYSTEM.

There should be a screw ON THE LINKAGE that allows you to adjust how fast the engine runs when the system activates - it is somewhere there among the throttle stuff. This screw is farther away from the carb body.

When you think you have found it, try adjusting it and see if the idle speed changes ONLY when the A/C is ON.

When you have found it, adjust it to 900 to 1000 rpm.

That way the engine will only speed up when the A/C is ON.

Hope this helps.

Dusky Lim
Dear Dusky,

what do you mean above about being easier to shift in traffic, pag mataas ba idle mahirap mag shift? ty