Idle adjust screw

[joyluck614]

My ride is a toyota corona silver edition with a 5k carburetor, medyo mababa masyado ang idling ko with makes the car vibrate too much, ask ko lang kung may nakakaalam kung saan ko makikita ang idle adjust screw sa carb ko and anong direction ko dapat iikot para tumaas ng kaunti idling ko.

Pag nakatayo ako sa passenger side ng engine, may nakikita akong color gold na screw sa ilalaim ng air filter cover sa side ng valve cover na aboout 45 degrees un angle, un po ba ang idle adjust screw? Thanks po uli mga tsikoteers!

[duskylim]

My ride is a toyota corona silver edition with a 5k carburetor, medyo mababa masyado ang idling ko with makes the car vibrate too much, ask ko lang kung may nakakaalam kung saan ko makikita ang idle adjust screw sa carb ko and anong direction ko dapat iikot para tumaas ng kaunti idling ko.

Pag nakatayo ako sa passenger side ng engine, may nakikita akong color gold na screw sa ilalaim ng air filter cover sa side ng valve cover na aboout 45 degrees un angle, un po ba ang idle adjust screw? Thanks po uli mga tsikoteers!

Dear joyluck614:

1st make sure to change your oil regularly as well as your air and oil filters - changing the fuel filter every 6 months or so wouldn't hurt either.

Have a tune-up done every oil change - clean and gap the spark plugs and make sure the timing is correct.

If your engine still has contact points, make sure they are NOT pitted and that the dwell angle is correct, and check if the condenser is still ok.

As much as possible, do NOT play around with the exhaust system if you want good power response and fuel economy - oversized mufflers look and sound great but perform poorly.

There are 2 screws that help to control your curb idle (that is the idling when the car stands still and the engine is running).

1st is the IDLE SPEED screw, you can find it by taking off the air cleaner assembly and then following the accelerator linkage to the side of your carb.

It is attached to the linkage system and moves the throttle plates (butterfly's) open or closed.

You will need a long flat screwdriver to adjust it (I know of no standard carb that uses philips head screws for adjustment).

Turning the screw clockwise speeds the curb idle up, counterclockwise slows it down.

The other screw (the bright yellow one you mentioned) is the CURB IDLE MIXTURE screw, it is yellow because that is the color of brass, which is generally used in valve materials.

If the idle system is working properly, generally you should not have to adjust this screw very often.

To adjust your mixture, use this procedure.

When you have done all the above, turn the IDLE SPEED SCREW clockwise to speed up your engine - because you said that it runs too slow.

When the idle speed is correct (check your tachometer), then you can set the IDLE MIXTURE screw.

Turn the screw (clockwise to close) in step of 1/4 turns until the engine starts to shake, - that's lean misfire, indicating that the mixture is too lean to fire evenly.

Procedure - turn 1/4th in, check for shake - if no shake, turn another 1/4th in, check for shake - if no shake, turn another 1/4th in and so on.

When engine starts to shake, back-off (turn the screw counter-clockwise) 1/2 turn and you set the curb idle mixture correctly.

Regards,

Dusky Lim

[joyluck614]

Dusky Lim,
Thank you for helping me out and all the tips you also gave me, worked out great, thank you and god bless

[duskylim]

Dusky Lim,
Thank you for helping me out and all the tips you also gave me, worked out great, thank you and god bless

Dear joyluck614:

You are very welcome.

Madali magbigay ng advice sa iyo because your car is easy to repair and the problem was relatively simple.

Best Regards,

Dusky Lim

[theshepherd]

Sir, what is the ideal idle speed for 12R engine? Mine reads 1000-1100. I want to bring it a lil bit down to decrease fuel consumption. Would 800-900 be normal?
Thanks in advance.

[duskylim]

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

[theshepherd]

Sir:
Thanks for the big help. I was able to adjust the idle speed and idle mixture myself. Brought my curb idle down to 800 without A/C.

But I was having trouble adjusting the fast idle. Can't seem to find the adjustment. I saw this nut with a flat screw slot in the center. Located beside the vacumm far side of the throttle linkage.

How do I post pictures here? I took pictures of it. If only I could post it here to clear things.
Thank you.

[duskylim]

Dear sheperd:

Do NOT touch that screw with flat nut and washer - from your description its the lockscrew for your throttle linkage assembly - taking it off will MIS-ALIGN your throttle shaft - disaster!

Look for a screw similar to or smaller than the screw you used to adjust the CURB IDLE with, that should be the one - it should be able to move the throttle linkage in an arc forwards or backwards, it will be pulled into action by a diaphragm.

The High Idle screw will NOT be on the secondary throttle linkage - it will be only on the primary linkage. And it will be mounted perpendicular (at right angles) to the throttle shaft axis - NOT parallel, coincident or concentric to it.

It is possible however that your carb may be one with out this HIGH IDLE (aka Idle Up) device - which means you have a very early model carb on your car!

A picture would be nice, but I've never posted one myself so I can't help you there.

Regards,

Dusky Lim

[theshepherd]

I see. I turned it 1/4 clockwise but nothing happened so I turned it back. Good thing I did.
Anyway, I don't know if the carb installed is early or not. I still have to find that screw. Idle without A/C reads 700-800. But with A/C on, 900-1000. But something happens when I start to drive it. The moment I get off on the gas pedal after stepping on it with A/C on, the rpm reads 1100. It won't get back to normal 1000 before I step on the gas. I think theres something wrong with the rubber that is connected from the accelerator linkage to the carb. There signs of fuel leaks. Not entirely streaming but stains of fuel leakage.
Can you give me some insight on this?
Thanks again.

[duskylim]

I see. I turned it 1/4 clockwise but nothing happened so I turned it back. Good thing I did.
Anyway, I don't know if the carb installed is early or not. I still have to find that screw. Idle without A/C reads 700-800. But with A/C on, 900-1000. But something happens when I start to drive it. The moment I get off on the gas pedal after stepping on it with A/C on, the rpm reads 1100. It won't get back to normal 1000 before I step on the gas. I think theres something wrong with the rubber that is connected from the accelerator linkage to the carb. There signs of fuel leaks. Not entirely streaming but stains of fuel leakage.
Can you give me some insight on this?
Thanks again.

Dear sheperd:

If the rpm goes up when you turn the A/C ON, then all is well - your idle up system (High Speed Idle) is Working.

If the rpm stays up until you step on the gas pedal, then you have a sticking accelerator linkage - there are several possible causes.

1) something is blocking the free movement of the carb linkage or accelerator cable - with the air cleaner assembly off (and the A/C on) have someone step on the gas and look closely at the accelerator cable or linkage - for something that may be interfering with its' free play or movement.

2) your accelerator pedal may have something (usually the carpet or floor mat) interfering with its full return, look inside the car underneath the dashboard at the pedal and cable linkage - there might be a problem there.

3) the accelerator cable is mis-adjusted and does NOT have enough free play to allow the carb throttle linkage to close properly.

To adjust the cable, there is a bracket with 2 nuts on it. One is a locknut, which you release to allow adjustment, the 2nd is the adjusting nut, which you turn to adjust the cable's free play.

Remember to re-tighten the locknut after adjusting the cable.

Check those things out - that's usually 90% of the problem.

You must make sure your accelerator cable and pedal is completely free in movement and that the carb linkage allows the throttle to snap fully closed, or else you will not only have the high idle problem but it will cost you a lot of gas.

In fact, there should be a little slack in the cable when it is in curb idle, the cable should NOT be pulling on the linkage.

Hope this helps,

Regards,

Dusky Lim