1990 Toyota Corolla A/F Mixture

HI there,

With the carby you only alter the idle mixture, the high speed mixture is basically pre set with jet size, with a rich mixture you don't get any real advantage, over rich will foul spark plugs, and cause idle problems, the choke system basically is an over rich running system, this does make cold starts easier, but with out the choke fast idle, the engine would soon flood and stall, fuel mixtures are best kept with in the normal operation limits, there is just no reason to play with them, if to lean you can overheat and damage an engine, to rich will start washing bores and cause premature ring wear, millions of $$$ are invested by car manufactures to get this right, why mess with it?

Mark (mhpautos)

Great advice by Mark, I would add:

A rich mixture will increase CO levels, and can cause engine damage if ran long enough.
This can be considerbly dangerous if running in garage (garage doors open), more dangerous that a car that is tuned proberly, as high CO levels can quickly overcome you in a very short time.

The only way to set the mixture would be with a wideband and dyno run.

I suppose you could get a remufactured carb set to factory specs, but you are basically shooting in the dark.

I"ll give you an example:

Client came to me several years ago after installing a nitrous system (75hp shot) on a V6 engine.
HP increase was very disappointing and he wanted to know why.
Took to local dyno shop, made a few base runs, found A/F ratio at 10.0 or less! (VERY RICH).
Replaced fuel jets down to lowest one we could find and still could only get A/F to 10.5.
Finally we increased nitrous jet size and got A/F to 12.3, car ran GREAT.
But without dyno run we may still be trying to find problem :).

Some aftermarket manufacturers sell wideband sensors that you can install on car, with seperate A/F gauge. This will at least give you a baseline to start, and some good info.
If A/F ratio is lean, it can quickly damage engine, like burn a piston.