How do I externally adjust/tune the 2 barrel carburetor on 85 Corolla

It sounds like the choke is either not setting or pulling off prematurely. In case you are not aware, when the engine is cold, depress the throttle pedal fully to the floor once and release to set the choke. When the engine starts, it should be at high idle until you kick the idle speed down.

I can't remember the last time I had to set the idle speed on a carb, but IIRC, the correct method for your car is called the "lean drop" method. You might want to try searching to see if you can find it somewhere.

Unplugging the vacuum advance from the distributor should not change ignition timing at idle. There should be a sticker under the hood that shows proper ignition timing, IIRC, around 10 degrees BTDC when warmed up.

For the 1986 Corolla, the timing is 13 degs. BTDC with all the hoses connected, about 5 degs. BTDC with one of the hoses disconnected and plugged. Some distributors have two hoses, others have three, and the hose to remove is not the one at the end of the vacuum advance unit.

I don't remember seeing that on my carb, but it seems like the stop for the throttle plate, in which case it should probably hold it open just barely enough to keep it from scraping its bore. .

If it's a screw that angles upward slightly, it's the main idle speed adjustment. Is it about 3" long with a head big enough to allow for finger adjustment? For 1986 Corollas it's set to 650 RPM for manual transmissions, 750 RPM for automatics.

After the engine is fully warmed up, adjust the idle speed screw for

700 RPM, the idle mixture screw for maximum RPM, then repeat both adjustments until turning the mixture screw won't increase the RPM. Then turn the mixture screw in to lean out until the speed drops to 650 RPM.

Engine warmed up, stop engine, hold throttle open, close choke plate completely by hand, release throttle, start engine without touching gas pedal. Turn the fast idle screw for 3,000 RPM.

ToyotaNation.com has great FAQs and forums,

has some manuals online for free (if you can't find the SR5, check the Toyota Corolla or Chevy Nova, which have the same engine and virtually the same carburetor). Some libraries and tech schools carry factory or Mitchell manuals, which are much better than the Chilton's and Haynes books, especially when it comes to stuff like carbs and fuel systems.

Dang...these things really do last don't they.

Some libraries and tech schools carry factory or

Thanks for all that great info; I really do appreciate it! A local library did have a Haynes, but it covered a lot of years, and the carbureter it showed and described was completely different from the one on my 1985. I never thought of calling the local trade school and inquiring about a better manual. Great tip!

Because I found a lot of posts suggesting Japanese/OEM ignition parts, I'm going to get rid of the Bosch plugs I put in it and use some Japanese ones instead. I did get my high idle corrected by following advice received here. Thanks again.

-Mark

Thanks for the advice, Ray, et.al. I did get my high speed idle and choke adjusted, with the help from this forum. Seems to start about as well as I can expect for an old car in 20 degree weather.

I have to keep the idle up around 1000rpm for it to be smooth and not stall, and the slow speed adjusting screw (turned out to avoid stalling) is rich enough to turn the plugs a light brown (more than just tan), so something isn't right. When I come to a stop the car still occasionally stalls.

Without disconnecting any hoses or anything, the timing light shows it is advanced way beyond the scale (which goes to 20 degrees btdc), so I've got to find out how to set this timing. I tried retarding it a little to see what happened, and the car wanted to stall when pulling away from a stop.

The compression ratio is only like 8.5:1 so there should be no problem with low octane fuel, yet it still knocks and pings some on 91 octane fuel.

Thanks again, and keep the good advice flowing.

-Mark

The engine is probably knocking and pinging because the ignition timing is advanced too far. Once you get the ignition timing set correctly, the knocking should subside.

Disconnect and plug the vacuum hoses to the EGR valve and see if the car idles better when idle speed is set correctly. If it does, the EGR is opening too soon or not closing properly. You can try removing the EGR valve and seeing if you can clean out some of the black crusty stuff inside.

I'd get the cheapest Densos available because that's what Toyota installed at the factory, and Toyota owns part of Denso.

Here's information about some other adjustments. I wouldn't tweak the throttle positioner or throttle position switch settings without a tachometer, unless they're really out of whack, but the throttle position switch should trigger when the throttle is opened just slightly, and the throttle positioner should make the idle increase noticeably but not by a huge amount. I once misadjusted the latter, and the engine would briefly rev up a lot when I took my foot off the gas pedal, causing the car to speed up instead of slow down. :(

Adjust carb mixture:

Adjust regular and idle speeds: Adjust throttle positioner: Throttle positioner diagraem: Adjust throttle position switch: Vacuum diagram:

But not that little plastic clip that holds the prop rod for the hood! I've had to replace it 4-5 times.

It's too bad the thing has only 75 HP. :(

I'd get the cheapest Densos available because that's what Toyota installed at the factory, and Toyota owns part of Denso.

Here's information about some other adjustments. I wouldn't tweak the throttle positioner or throttle position switch settings without a tachometer, unless they're really out of whack, but the throttle position switch should trigger when the throttle is opened just slightly, and the throttle positioner should make the idle increase noticeably but not by a huge amount. I once misadjusted the latter, and the engine would briefly rev up a lot when I took my foot off the gas pedal, causing the car to speed up instead of slow down. :(

Adjust carb mixture:

Adjust regular and idle speeds: Adjust throttle positioner: Throttle positioner diagraem: Adjust throttle position switch: Vacuum diagram:

In two of the jpg pics you posted links to, you have handwritten a note re an "acceleration hesitation modification". Can you explain what you did to, I presume, eliminate or improve the hesitation problem?

Thanks, Wayne

There are three overlapping technical service bulletins from Toyota about this, and they make a noticeable difference, although they won't turn a 70-75 HP engine into one that gives neck-snapping acceleration. :(

Bulletin 11-21-86, issued Nov. 1986, to reduce hesitation during warm- up, applies to 1984-1986 FWD Corollas and consists of simply adjusting the float so that the fuel level is at the upper allowed range in the sight glass and then readjusting the mixture as described in one of the figures. BTW for 1984 and 1985 Corollas with automatic transmissions, the idle speed should be 800 RPM, not 750 as with 1986 and 1987 models.

Bulletin Volume 8, Section Engine, # 018, issued May 1986 for

1985-1986 FWD Corollas, consists of installing a restrictor in the vacuum line between the R port of the EGR vacuum modulator and the EGR port on the carburetor. Also the ignition timing is changed from 5 degs. BTDC to 3 degs. BTDC while a certain hose is disconnected and plugged.

Bulletin Vol. 8, Section Engine #030, issued Feb. 1987 for 1985-1987 FWD Corollas with automatic transmissions, involves making the above changes plus also changing the accelerator pump arm, main carb jet, coil spring in the vacuum diaphram that opens the secondary port, and possibly also adding a restrictor or one-way valve between the Q port of the EGR vacuum modulator and the EGR valve, but nothing is mentioned about the latter in the text, only in one diagram (black side of the restrictor/valve goes toward Q port, light-colored side to EGR valve).

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Thank you for the very detailed information! Much appreciated.

larrymoencurly, Thanks so much for posting these wonderful photos from the Toyota Corolla service manual! I couldn't make them work at first, until I realized I had to cut and paste the URL and remove the inadvertent space that appears on groups.google.com, so the link would work. I just did that

Also, I found out after looking at your emissions pics that I must have a California spec car, because there is no high altitude conmensator (HAC) on my car, and the air feed to the catalytic converter is totally different than on the federal model. I live in Pennsylvania, and didn't see any under the hood sticker that told me otherwise, so I just assumed it was federal emissions. Any chance you could post the component layout diagram for a CA emissions 85 corolla w/ 4AC engine?

The Haynes and Chiltons books I got are just worthless because they don't address all the variables that are possible (for different years, emissions equipment, drivetrains, etc), the pictures are poor, and the information is downright wrong.. I couldn't find a factory manual for my car, but after seeing how wonderful your scans were, I immediately bought a manual for an 83 (although my car's an 85) off ebay for $30 (hopefully it will work for most things.)

I'm buying the OEM factory manual for any vehicle I buy from now on. Thanks for showing me the light!

You mentioned the factory service bulletins; thanks for such complete reporting of valued information. How does someone get access to factory technical service bulletins, other than paying the dealer to service the car?

The fix for the clip that holds the hood prop rod that I devised was to Gorilla Glue a 1 inch length of fuel hose to the top of the broken clip, then cut a longitudinal slice out so the prop rod can sit in the hose. It is the only repair to this Corolla that I've be able to competently execute on my own.