Is there a good document to show the way. I just hooked up an AFR meter and would like to give it a try. As it is, my readings show that I am running toward the rich side.

 

At idle? Cruise rpm? or WOT. All three of these are adjustments in the carb but are different. The idle is the idle mixture screws and WOT could be Jet size or power valve. Depends on what carb you are using. Post up some of your readings at different rpms and throttle settings and then we can adjust from there.

 

Idel@750rpm= 12.5
Crusing 50mph@2200rpm= 12.5

I just adjusted the idle screws , was at 1/2 turn out. adjusted both 1/8th turn in
New ready at idle= 13.5

 

start here

http://www.innovatemotorsports.com/resources/Stan1.php


the forum is down right now but once up you can spend hours reading there.

there's plenty of knowledgeable members here that will help if needed.

Neal

 

what carb you runing?

 

the following link is from engine builder magizine on tuning the a/f mixture with a wideband a/f meter or a exhaust gas analyzer http://www.enginebuildermag.com/Arti..._equation.aspx

Henry @ olescarb

 

Thanks for the links.
I am running a Holley spreadbore 4175 carb Vac secondaries.
The AFR I am using is a Glow Shift Wideband with a Bosch LSU 4.9

 

13.5:1 at idle isn't a big deal. I wouldn't worry about it as long as it idles well.

You want to concentrate on getting your cruise AFR into the 14s. You also want to check WOT and make sure it hovers in the mid 12's. Many have found their aftermarket carbs have a "backwards" fuel mix, 12:1 at cruise and 14:1 at WOT. You want to make sure your WOT is good before trying to lean it out at cruise.

 

Thanks zwede, thats the numbers I was looking for.
It stays steady at the 12.5 no matter what cruising speed I have been testing at (40mph-60mph).
I have not been able to check wot for any real distance yet. Should be able to do that tomorrow.

 

god info

 

That guy who wrote the article knows what he is talking about, I like someone who knows something and doesn't repeat the same old wife's tales over and over

Our gen 1 engines like it rich, you try and get too high into the 14's at cruise and you will start to have lean misses

 

I copied this from my Edelbrock carb installation manual.

BASIC ENGINE REQUIREMENTS
The spark-ignition 4-cycle engine burns a mixture of AIR and FUEL. The air is controlled by the driver’s operation of the throttle. The fuel is mixed with the incoming air by the carburetor. The Ratio of AIR to FUEL is the AIR/FUEL Ratio (A/F). This is a ratio by WEIGHT; if 12 pounds of Air are combined with 1 pound of Fuel the A/F is 12:1, or more commonly, A/F = 12.
Despite the enormous variety in engine designs, virtually all (spark-ignition 4-Cycle) engines have very similar A/F Ratio requirements. For fully warmed-up engines, the range of A/F is:

A/F RATIO CHARACTERISTICS
5 RICH BURN LIMIT: Combustion is weak/erratic.
6-9 EXTREMELY RICH: Black smoke and low power.
10-11 VERY RICH: Some supercharged engines run in this range at full power as a
means of controlling detonation.
12-13 RICH: Best power A/F: Un-supercharged WOT.
14-15 CHEMICALLY IDEAL: At 14.6 the A/F is at the theoretical ideal ratio with no
excess fuel or oxygen after combustion. Good A/F for part
throttle cruise and light to moderate acceleration.
16-17 LEAN: Best economy A/F ratio. Borderline for part throttle
drivability (worse than borderline if EGR is used).
18-19 VERY LEAN: Usual lean limit (Driveability).
20-25 LEAN BURN LIMIT: Varies with engine and system.
Even though engines will run anywhere between 5 and 25 A/F, the usual target values for an unsupercharged engine are a fairly narrow range (Figure 1). A/F is about 12.5 for the WOT and 14.0-15.5 at part-throttle cruise. An intermediate value of about 13.5-14.0 is usually used for mid-range power (non-WOT acceleration).

 

I would do a few WOT runs and log the data. If the AFR is anywhere in the 12s or even 13.0, leave it alone....no reason to open Pandoras box here....

I you try to lean a carbuerated engine out to anywhere near 14.0 AFR at steady cruise you will get lean surges, misses and stumbles all over the place..... Fuel Injected engines are more forgiving of this but even so I never tune them that lean.....I tune a lot of fuel injected 4cyl motorcycles and anything leaner then 13.5 afr they start acting up....

I usually shoot for mid 12s-13.0 for steady cruise and WOT....but for peak power, you really need to jet it at the drag strip so you can effectively measure the gains....a chasis dyno can accomplish this also but often you will find that what the engine wants on the dyno is not what it wants on the drag strip....they almost always want more fuel out on the track.

Idle afr is usually good at 13.5-14.0 after it's warmed up. Adjust your idle mix screws to obtain the highest engine speed....a vacuum gauge is good for this. Once you get the vacuum and speed peaked...you can lower your idle speed with with the idle speed screw, then check your AFR.....I bet it will be around 14.0-14.5.......some engines idle smoother with a richer idle... 13.5, you're good to go....

Don't fix what ain't broke....if it runs well, be happy!

 

what parts of the carb control light throttle and cruise?

cheers

dave

 

On a Holley, mostly the IFR (Idle Feed Restrictor). A traditional holley only has 2 circuits, main and idle.

 

ive got a quickfuel 750 double pumper, mech sec, would that have idle feed restritors?

 

Yep.

BTW, some VERY good discussions on Holley (and derivatives) tuning over on the innovate forums.

 

ive also got a blowthrough version of the quickfuel 750, am i right in thinking that has the idle feed restrictors filled up, blocked??

cheers

dave

 

It has been a while but I finally got the time to revisit this.
Idle is in the 12.5 range.
Cruise is in the 12.5 range any where from 45mph and above 80mph.
WOT starts out in the 12.5 and increases to around the low 14's for a short time until it gets going, I figure this is the excellerator pump circut being I have that tuned real lean. once it starts hitting the area that the secondaries open up it drops hard into the low 11's. By then I am hitting above 3500rpm's and about 75mph.


I already changed the secondary metering plate from a 54 to a 49 a couple of years ago when I had the car on a dyno and it showed the WOT to be in the low 10's.

I would like to see the cruse afr to be closer to 13.5 range. If I change the metering plate again I know that will change my WOT but to what size?
Will this effect the cruse afr or do I need to change the main jets too? If so how many sizes should I drop them, 1 or 2? I do not know what size is in there until I get a chance to take it apart.