I borrowed a AF meter from a friend and was wondering what is the best process for reading and setting the mixture.

Can I take readings at idle and hold the throttle at 3k and take another reading or do i need to drive it with it under load?

based on readings which adjustment do I move first static or dynamic?

I do an idle adjustment and an adjustment for readings under load.

idle means nothing beyond emissions (and not much)

search... there has been 3 threads about this in a week
but it absolutely has to be under load..............


and really redline is the only number that matters.
(race car..... but also its the only one that hurts your motor)_

OR, wasted fuel and washing down cylinder walls. (That's why I do an idle adjustment.) You don't need to be running 9:1 at idle, do you?

The big question is what jets are you checking with the AF meter, idles or mains? Lets face it, idle adjustment is 4 screws with the butterflies closed. You're not going to be washing down the cylinder walls at a stop light. What's more important in a street car is off idle when you're running on the progression ports (idle jets).

Just to throw another wrench in the works is that a smooth transition to the mains depends on idle jet size, vent size, ET tube selection and main jet size. You may have to compromise on your AFR in some throttle positions in order to obtain the best transition. The question you'll have to ask yourself is how good is good enough.

I know a lot of people with AFR gauges in their race cars.
Truth is that if you dont log the data, then they are of limited value.

You need to see the AFR trend at WOT.
Glancing at the gauge when you get the chance doesnt cut it.

Got this from one of Chris Foley's posts

in A:F ratio, you want to see:

13.5-12.9 on the gauge while accelerating or climbing,

12.8-12.5 at WOT,

and 16-17 while cruising, going downhill or decelerating.

Right now I am in those ranges with FI. A little richer on WOT as I can get to 11.5 at times. But seems to run well in these ranges.

Mike what numbers are you seeing at idle?

I am getting 27-28 range.

Acceleration and WOT I am close but the idle numbers seem way too lean.

Wow that is really lean! I am at 13 to 14 at idle. Are you running FI? If so you may want to richer the idle mixture on the ECU.

I am running L-jet are you running D or L?

I am not aware of an adjustment on the ECU on L-jet but there are 3 adjustments on the air meter. static, dynamic, and mixture(which is used to adjust the mixture at idle as I read form an l-jet procedure that has been posted on several sites.

As I understand the next step in this current state is to richen the mixture via static to get proper numbers at idle then back off the dynamic to bring the accel and WOT numbers back to where they need to be, then fine tune the idle with the mixture screw.

You are correct. I am running D-jet which has the knob on the ECU. My gauge does not go to 28. I would not think it would idle all that well if it was really running that lean.

Exactly right, it barely idles right now

I don't run carbs, so arguing about idle mixtures with carb guys is a waste.

Idle adjustment on an L-jet is very important. It is the starting point for the fuel curve.

My L-jet #'s are:

Idle 14:1
Acceleration: 12:5-13.5:1
WOT: 12.5
Cruise on hwy: 15.5-16:1

If I richen the idle numbers, the rest will follow. I would like my idle to be around 13:5:1, but if I do that my WOT goes into the 11's. So I always work on getting the curve right and then adjust the idle after that work is done. It will take a couple of tried to get it where you want it.

I have 2 AFM's. One set up for road trips (leaner for gas mileage :31mpg) and one set up for racing (richer : 22mpg)

I read this 5 times before attempting an adjustment. Lots of info.
http://www.itinerant-air-cooled.com/viewtopic.php?t=7761

I have studied that
One problem i have run into is when I richen the static I have had problems getting the fuel pump shut off arm bent to where it doesn't hit the contacts in the switch that shuts the pump off. Don't know if I am bending this improperly or what.

Jake had mentioned in a previous post about possibly needing to drill a hole in the throttle plate to let more air into the engine, which I haven't done yet.

but I just posted this into the original thread hopefully he may reply with some advice/confirmation

Idle is somewhere between 300 and 500 rpm with AF reading 26-28
If I crack the throttle and bring the rpms up to 900 I get numbers closer to 16-17 (this was just a first glance) which lead me back to the 1/8" hole in the throttle plate.


Does this point to needing that hole so I can even get the idle up to where the AF is giving relevant logical readings?

Wow! Never heard of drilling a hole in the throttle plate. Not disputing Jakes theory, but I'm not sure I'd try that before working through it a bit more, or having a spare throttle body.

Jake knows more about type 4's than most. My input is based on what my engine likes.

What about your idle adjustment screw in the throttle body? How is the adjustment on that? Closed, open, in between?

I have messed with the bypass screw but it doesn't make much difference. Once it is warmed up I get more response out of the screw.

I do have an extra TB so I might give it a try.

Drilled hole in the TB and had noticeable improvement on idle.

got numbers as follows for AF ratio

Accel. - 12.4 - 13.7

WOT - 12.1 - 12.7

Cruise - 12.6 - 13

Coast - 12.9 - 13.3

The cruise isn't as lean as what I have seen is desired.

So which adjustment do I go about to bring that in line? Static or dynamic ? I have not moved the mixture screw on the outside of the meter yet it is set 4 1/2 turn open.

Idle numbers are still all over the map cause now it won't come back down off of idle Unless you load the engine and pull it down that way, so it idles around 1200-1900 rpms
At around 1200 I am seeing 14

The throttle body of the L Jet has 2 air connections that originally went to the distributor. In my car both have been plugged, a Mallory Unilite was installed. Could one of the air inlets be comparable to drilling the hole ?