1990 Toyota Corolla A/F Mixture

Tiny
JACKOLSON
  • MEMBER
  • 1990 TOYOTA COROLLA
  • 4 CYL
  • FWD
  • MANUAL
  • 80,000 MILES
What's the problem of running a rich A/F ratio? What does "rich best torque" means and how do I set it up like that.

I know on overly rich mixture can be expensive on the pumps and bad for the environment, but please, without considering fuel economy and emissions, what are the mechanical disadvantages of a rich mixture? And what good does it have to run a rich mix?

I'm running a carby-engine, no O2 sensor, no MAP, no electronic everything, no ECU, no ECM, no Air Flow sensors, no nothing of that. So I'm not worried about messing up those things. I just have the old school setup.

Thanks and more power.
Do you
have the same problem?
Yes
No
Friday, December 4th, 2009 AT 9:28 PM

4 Replies

Tiny
MHPAUTOS
  • EXPERT
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)
Was this
answer
helpful?
Yes
No
Friday, December 4th, 2009 AT 9:40 PM
Tiny
MMPRINCE4000
  • EXPERT
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.
Was this
answer
helpful?
Yes
No
Saturday, December 5th, 2009 AT 7:02 AM
Tiny
JACKOLSON
  • MEMBER
Great advise indeed, thanks.

But the previous owners of my cars seemed to care less and they in some sort of way altered the A/F and Idle settings. What you said is exactly what I'm looking for, a straight answer. What setting should I then go for and how can I get it there. I only have access to a gas analyzer, I can't seem to find a dyno here in my country and nope, I can't find a wideband O2 sensor either, been searching since last month. I wanna get this over with so my car can run free of worries. What sort of figures am I looking forward to get on the gas analyzer? BTW, my choke is disabled by the previous owner and I don't think I need it here in our country, doesn't get cold here in my place. Otherwise, okay I'll have it check to restore it. Thanks again, more power.
Was this
answer
helpful?
Yes
No
Saturday, December 5th, 2009 AT 11:33 AM
Tiny
MMPRINCE4000
  • EXPERT
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.
Was this
answer
helpful?
Yes
No
Sunday, December 6th, 2009 AT 6:52 AM

Please login or register to post a reply.

Recommended Guides