Air/Furl mixture with 80 Corolla

Hi,

I have a RWD 4 door, 1980 model Toyota Corolla. It was purchased in Saudi Arabia and is now in India (since '93)

It's done about 75000 only and was lying idle for a while. I've started using it again now and was trying to tune the air/fuel mix, since lately it was going fast or slow in idle on it's own.

I need help with this since I am unable to understand how to get it right. There are two screws behind the air filter. I fully tightened the lower one and then moved it about 1 and a hlf turns counter-clockwise, below that, the car dies out. The other one, the one on top/easily accessible one used to make more differnce to the idling earlier, but now it doesnt make much diff. I've kept it half way for now, not sure where it should be.

But after I did this, my car is soooo much smoother, earlier it was sluggish. This is definately the result of my twiddling with the screws. My priority is to get good mileage, and I think this is not helping.

I know one screw is for the air/fuel and the other for idling, but dont know which is which. I need help figuring out how to tune this up for good mileage on my own. It's not easy to get a good mechanic for these oldies where I live.

thanks, Sam

Reply to
sammy
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This advice is coming a little too late, but you probably should not have touched the air/fuel and idle speed control screws because it is unlikely that they were causing your problems.

If the car has sat for a while, the carburetor and linkages are probably gummed up from varnish buildup, which can be cleaned with some aerosol carburetor cleaner. My guess is that the choke was sticking. To start a cold engine, fully depress the accelerator pedal once, which should close the butterfly valve (plate visible from the top of the carburetor). As the engine warms up,the valve should open.

Reply to
Ray O

This is EXACTLY what I was going to say!!! ;) NEVER NEVER fool with the air screws (I did once and lucked out...the car actually ran when I was done). With the exception I was going to mention a cracked vacuum line somewhere...

Reply to
hachiroku

One of my first experiences messing with a carburetor was when I was about

12 years old. I thought that our Lawn Boy mower wasn't running right and a tune-up was in order. ..

I started at noon and was still futzing with it when my dad came home around

7:00 PM. He got it going after dinner, and I was mowing the lawn in the dark.
Reply to
Ray O

Jesus, you guys make carb tuning sound like rocket science.

All tou need to do is find the base settings for idle and mixture. If it doesn't start, try half a turn higher on idle, until it does. It if splutters but won't run, try richening the mixture until it does, or dies trying. Then try leanign it a little. A CO meter is useful, but not essential. If you get smoke, what colour is it, the blacker it is, the more you need to lean it out. Once you have it running, then you can get things straight mixture/speed wise.

But always, always use the factory base setting as a starting point. It only gets tricky when you are trying to synchronise and balance multiple carbs.

Reply to
Sleeker GT Phwoar

Reply to
Ray O

But it says right in the manual: "Do NOT f@ck with the Carb Screws!"

Honest, it does!

Reply to
hachiroku

BTW, did you ever answer my question about the Meatballs?

Reply to
hachiroku

Well, it's starting and running really smooth. I adjusted the lower one till it did. But the other one..I think idling (and if you guys have know which is which, let me know too!) doesnt seem to be having any effect. Earlier it used to.

Is it really hurting my car to drive it this way? then I'd rather keep it home till I get this sorted out. I know now that the air screw is not be messed with, but now that I've done it and I can't CTRL+Z it....the help I need is on how to set it straight again. I dont have the manual with me, no idea on where to get it either...at least not immediately. So I don;t know the factory setting, and I doubt it was at the factory setting...it's 25 years old!!

thanks! :)

Reply to
sammy

No, although a misadjusted carb can cause poor fuel economy.

Actually, unless you mess with the screw, it will retain the factory setting.

With the engine warmed up to operating speed, idle speed should be around

550 to 600 RPM in neutral for a manual transmission and around 700 RPM for an automatic in drive with the brakes depressed, all accessories turned off.

If the car is running smoothly and fuel economy is not too bad, just enjoy the car!

Reply to
Ray O

Thanks Ray. I don't have the second meter to show me the RPM, just the speedometer. Though I know how the engine sounds when it's running too fast or too slow, though I cant really tell what the ~ RPM might be for that sound.

And oh, I did figure out that the top screw is for idling the other is the air-fuel mixture. It seems the idling screw was all the way out, and the car was still idling, which means the air-fuel was quite high and today I noticed that on the floor behind the exhaust, there was a spray of black dots, I dont know what that means, but it sure doesnt look good!

For now I have turned the air-fuel screw counter-clockwise a few turns and increased the idling, as of now, I'm going to reduce it as much as possible while making sure it idles well and starts well. From there I'll tweak it if the economy is bad.

Do you think this is a good strategy, or do you suggest something else?

Reply to
sammy

The spray of black dots is probably caused by a rich air/fuel mixture at startup. When an engine is first started, it takes a while for naturally occuring condensation to burn off. While this is going on, it is normal to see water dripping from the tail pipe, especially in cooler weather. If there is soot in the exhaust, the water will be black. Some soot is normal but a lot of soot is caused by an over-rich air/fuel mixture.

Great strategy if you do not have a tachometer!

Reply to
Ray O

I don't know about thet, but I'd rather tune a Jet engine...

Reply to
hachiroku

"Ray O" wrote in news:ac6fa$42b901b7$180fead6$ snipped-for-privacy@msgid.meganewsservers.com:

Well, I'd disagree. If the engine is running rich enough to adversely affect gas mileage, you're also running the risk of washing oil off the cylinder walls and diluting your oil. This will result in rapid ring wear.

Reply to
TeGGeR®

Yes, but if it was THAT rich, wouldn't it flood easily or have other symptoms?

Reply to
Ray O

Sure, and these settings only affect the idle range...the cruise and high power range is controlled by the a non adjustable jet size, certainly true on older vehicles, although possibly not on ECU equipped cars.

But I'd be very surprised if you can manually change the mixture for high power stuff. That's a very sensitive range 'serious damage wise' and I'd be most surprised if they'd allow mere mortals to futch with it...

Reply to
Gord Beaman

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