hey guys i am tryign to tune my carb right now for the best milage and performance and wut not and i wunt to get it so its not to rich and not to lean. now its a 750 edelbrock and i have went one step lower with the metering rods and it seems to run real nice. i can;t smell exhaust anymore but i think it might still be rich and i can;t tell. so is there a way to tell if its rich or lean? i am gonna be hookin a vacum guage up to set the carb also. thanks guys

 

A good indicator of it running well (not rich/lean) is what temperature the engine runs at.. if its at or very close to 220* you're good to go.. if its quite a bit colder than that, lean it out a bit.. if its alot hotter, then you're too lean, richen it up!

Also, if when you get warmed up to running temp, let the engine idle, then stamp the gas to the floor for just a second. If it bogs down before it revs up, you're running a bit rich, so lean it out a little.

Hope that helps.

 

tuning based on temperature is generally not all that effective, especially if your trying to do it with the stock gauge, which is often off.

An easy way to tell is to take it out and romp on it a few times, then pull a plug or two right after. If the plug is all sooty and or wet, your rich.

if you wanna spend about 35 bucks, you can get a digital Air Fuel guage from summit, thats about the best way to get an idea of where your at...

Eric

 

ok now i was lookign at the air/fuel guages in summit and jegs and the autometer ones just say rich, lean, and stoich. now is stoich like the perfect place to be? also on these guages is it 3 bars liek the one rich bar will light up or the stoich bar or is it a needle? also for under 50 bucks any1 suggest a better guage then an autometer? thanks oh yea an di woudl just need to hook it up to a stock o2 sensor right? caus ei have no comp in my car

 

the autometer one hooks up to your existing O2 sensor. Stoich is where you want to be with it. Obviously it's not gonna give you actual numbers, but it's a good reference point. There is no needle, just LEDS that light up in the given areas...

In the Summit catalog there is also a digital one made by either cyberdyne or dakota digital (i forget) thats like 30 bucks. I've never seen or used it though so i can't comment on how it works...

Eric

 

Here is a better A/F ratio guage and lots of good info in how to use it.

http://www.speedshop.org/store/Scripts/default.asp

 

your links no good, also with the autometer is it only 3 LED's that light up, liek one for each or is it kind on a scale so u can se if your way rich or wut?

 

its a scale, there is several LEDS for each condition used to show magnitude...

And F-BIRD's link works for me....

Eric

 

Ok.. For starters that carb if working correctly should be fine...

Leaning out a carb can have the opposite effect. A properly functioning carb is designed to work as a unit inside and out.
Leaning it out can cause you to step further into it. The farther you have to step into the throttle the worse the mileage is regardless of what you do to the carb. Fuel will be drawn to satisfy the needs for the motor. The wider the openings the more air will flow and the fuel flows with it. Thats why keeping your foot out of a carb gets the best mileage regardless of if you have a 2 bbl....

The only real mods on that carb I'd make is maybe accel pump height and I'd drill the squirters out so it looked like 2 people pee'n. mileage would suffer but it would be off the hook when you nailed it

The Ideal fuel mixture is stoich .. or stoichiometry.

This is a fuel mixture of 14.7 to 1 ... In a carb situation you have only one throttle angle or possition you might be able to capture that but chances are greater than not that your spinning your wheels. The O2 sensor on a injected system changes values very rapidly in an attempt to keep the mixture at stoichiometry.
In your situation every speed change and throttle angle will take the ratio to a diffrent place so Stoich is not per say very likely.

If it was me.. I'd put on a Holley 750 instead of the edel... Keep my foot out of it if I wanted better mileage and get another car if that is my daily driver cause if your driving daily what I'm reading as your signature your mileage will never be real special. If it stinks.. It is either carb problem or maybe even normal.. 8-)

Good Luck
From a fuel systems specialist

 

Don't mean to burst your bubble but......

The ideal A/R is not strouc**(spelling) or 14.7:1
that is the chemically correct ratio that consumes all the oxygen and fuel. (Theroretically)
The ideal Air / fuel ratio for best mileage is quite a bit leaner.
How lean you can run your car at cruise depends on a lot of factors but mileage will always be better at a a/f ratio leaner than 14.7:1

Some car like old honda civics can cruise at 17:1 or leaner.

Computer controlled emissions cars try to maintain 14.7:1 because that is the ratio that gives the best emissions compromise with a 3 way cat and AIR injection pump.
It also happens to be where automotive O2 sensors
"switch" allowing a computer to crowd or maintain that ratio
in closed loop mode.
Full throttle operation requires a richer mixture to cool the chamber a bit, suppressing detonation and ensuring a even/ combustable mix throu-out the charge
Back to carbs:

Leaning out as carb that is a little too rich is the way to
save gas. Too much fuel jetting will result in extra fuel and o2
left over after burning and higher emmisions and inefficiiency.
Being too lean can cause this too.
Its all relative.

Many/ most universal type carbs like a edelbrock 600/750 or a holley 3310 etc are calibrated to be a little rich at cruise "out of the box"
(heir actually tuned to be a little rich at sea level.)
Being a little rich is safe ( won't do any damage)
and allows the carb to work fine when bolted on to most any ones typical performance car. (Customer satisfaction)
You can further fine your carb to your car with impressive results.
By carefully adjusting the jetting and accelerator pump calibration.
Edelbrock carbs often show a fuel perculation problem
in hot weather especialy with ethanol enhanced fuels.
Try a wooden carb spacer to reduce the heat soak.
this is usually/ many times what makes these carbs "stink".

I've been tuning these carbs and others on many cars, trucks boats for some 30+ yrs.
Wether that makes me an "specialist" is relative too I guess.

 

How do you lean out the carb? I'm pretty new to carbs, and I see the two screws on the front of the carb, with the idle screw to the side. Which way do I turn the screws to lean out the mixture? and why are there two of them?

<EDIT>

Haha, ok, nevermind. Did a little search, and got it.