Re: How do I externally adjust/tune the 2 barrel carburetor on 85 Corolla
> How do I externally adjust/tune the 2 barrel carburetor on 85
> Corolla? My SR5 has the SOHC 4AC engine and is rear wheel drive. USA
> Federal emissions model.[/color]
> 1. Very hard starting when cold, won't accept throttle until engine is
> fully warmed up.[/color]
> 2. Hesitates/misses at low RPM when throttle is opened, especially
> just off idle, like when pulling away from a stop sign (engine
> sometimes stalls unless throttle is applied VERY slowly, especially in
> cold weather).[/color]
> 3. Engine knocks and pings on gas with octane rating below 91 (when 87
> octane should be sufficient.)
> 4. I have access to a timing light, and I see the marks on the
> flywheel pully and block, but am not sure how to correctly check the
> timing, because I plugged two vacuum hoses that were attached to the
> distributor advance unit and the timing was unchanged (and it should
> have dropped back), so I must be missing something. How do I
> correctly set the timing?[/color]
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 replaced: ignition components (plugs, wires, rotor, distributor),
> fuel and air filtes all recently replaced with aftermarket parts. I've
> tried some fuel system cleaner that I added to the tank. Exhaust
> system appears fine, muffler is new. Everything else seems to be
> There's a screw that is on the opposite side of the carb from the
> throttle cable. It seems to be a "stop" for when the throttle is
> closed, adjusting the amount the throttle is open when the engine is
> not running. How is this to be adjusted?[/color]
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.
> There's a slotted screw that is threaded into the body of the carb
> near where the cable assembly is connected, (on the adjacent side of
> the carb) This seems to adjust the idle. How is this to be adjusted?[/color]
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.
> I drilled out the plug over the slow speed mixture screw, but don't
> know the correct setting.[/color]
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
> I see the high speed idle screw is part of the throttle cable linkage.
> When/how is this to be adjusted?[/color]
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, [url]www.autozone.com[/url] 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.