Setting the idles and fuel/air ratio

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jhdeval

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Okay so 2 weeks ago I set my idle and fuel to air ratio and everything is great when the headlights are off.

The service manual states to:
pull the high idle off the lowest step
set the low idle to 550 RPMS.
adjust the fuel air ratio to get the highest rpm
reset to 550 and try again

After that is set and there is no more adjustment:
set the bring the high idle to 750 rpms

The instructions do not indicate turning on any draw items like the alternator or ac compressor. Should I have them both turned on while doing the setting? If so how will that affect the idle when they are off? Will it increase like I expect it to?
 
I don't think you would get a different answer on the fuel air ratio with or without the headlights. If you need to speed up the idle a tad to compensate for the headlight drag, go for it. I don't think you need to readjust the mixture, just increase the idle speed. Also don't get too hung up on the numbers. As long as it idles good for you and doesn't want to creep too much while idling in drive (assuming automatic), you should be fine.
 
Headlights should not affect idle that much. Biggest effect on idle speed after obtaining a proper "curb idle" is if you have an auto, in drive.

My Dad, rest his soul, was one of those people who always wanted the slowest idle possible. His always had his old Chivvy pu with straigh 6 idling at about dead slow. I'm the opposite. I don't mind if the idle is a little high. My little 318, with a really mild cam, used factory (low stall) converter idles at 8-900 in neutral, and that's the way I like it.
 
Well I had the idle set way high to compensate before so it drove fine but the gas mileage was killing me. Thats why I adjusted it. I know the numbers are rough guages I just needed a start point and it worked out. So if I bring the idle up I do not need to worry about the fuel air?

My main concern was if I reset the idle with the headlights and ac on will my idle jump to high when they are off?
 
I do have an auto and that is where I see the rpm drop. I loose about 100-150 rpms give or take. My tach is kind of small so hard to tell exactly.
 
If the idle changes in an unmanageable level, disregarding AC and lights, it may be an indication of poor tune, IE not enough timing advance, incorrectly adjusted carb, or other problems such as a worn engine or vacuum leak.

If the AC is too big a problem, you can "rig" an idle solenoid, activated by the AC clutch, which will boost idle speed with the AC clutch engaged.

So far as headlights, I don't see a problem. Many of these old cars dimmed lights somewhat, but this can be improved. It might be the old bulkhead connector problem, or other electrical problems.

One big improvement can be had by going to the later model "squareback" alternator used in the mid 70's which you can use with your old style regulator by simply grounding one field connection on the squareback

It may also be that there are other problems, such as a problem with the alternator (internal problem) that causes it to not output full current.
 
67dart273 the headlights do not dim I set them up on relays straight off the battery. They are good. As for the worn engine. I am looking for either a new slant block or a 318/340 to replace it with. I am just trying to keep it going for now.
 
/6 ideal idle is 8 hundred.. a tick or 2 below 1.000 rpm.
Let the water and oil pump do there job..
 
65LoveAffair I would not think so. The difference from what I understand between a 170 and 225 is the head and the crank rods (attach the pistons to the crankshaft) are slightly longer.
 
Are you having a problem or just asking what the correct way to adjust the idle would be? Your first post states that "everything is great when the headlights are off". Does that mean everything isn't great when you turn them on?

I've never had an A/C before...does it drop the idle a little bit when you turn it on? I would guess it probably does. The headlights should have no noticeable effect. If the idle drops a little bit with the A/C on, then I would adjust the idle with it on because you don't want to have it idling as low as possible and then turn the A/C on and have the car die.

I have mine idling at about 550rpm in gear and 700-750rpm in park. It doesn't get cold enough to snow here and my engine has good vacuum so I try and run it as low as possible year round to save gas. You should be tuning with a vacuum gauge to get the most vacuum as well. You want to be around 20hg on the gauge.
 
I forgot about the vacuum gauge thank you.

ESP47
It is not necessarily a problem but my idle would drop with the ac and headlights on. I know this is caused by the extra draw from the alternator and compressor. My question was whether I should set the idles/fuel air ratio with those draw items on and if so how would it affect my idle when I turned them off.
 
I can't remember for sure but turning the headlights on while doing the idle adjustments sounds kind of familiar. I feel like I've read that in the service manual but I didn't do it because my headlights didn't make a difference in my idle speed.

Before you added the relays, your lights would be dimmer during idle and they would get brighter when you hit the gas right? Now with the relays they stay bright whether your idling or in the gas? That could be why you see a bigger fluctuation in your idle speed but that's just a guess on my part. I don't have the replays so I wont notice it because by time my lights are getting brighter, I'm already on the gas and idling doesn't come into play anymore.

I would turn on your A/C and headlights when doing your idle adjustment. If you don't and you adjust your idle as low as possible, the car could possibly die at a stop if you happened to have your A/C and/or headlights on. How much does each thing drop your idle? If you do the adjustment with them on, then obviously your idle will raise a little bit when neither one is on but you'd rather be idling 50rpm or so high than 50rpm low. 50 high is barely noticeable, 50 low could be the difference in the engine stalling or not.
 
I wouldn't worry about idle speed too much. I set it as low as I can, so it doesn't want to die in "D" w/ AC on, and I go fairly lean. I recall that later cars were set to idle much faster. A boss had a new ~1974 Buick that sounded like it idled >1000 rpm in "P". I think they did that for emissions reasons, maybe because the carb was set so lean it would die in "D" otherwise. There were lots of driveability problems in brand-new cars as emission fixes were kludged onto carburetors in the late 70's and early 80's.
 
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