AFM ADJUSTMENT w/o gas analyzer

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Gypsie
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AFM ADJUSTMENT w/o gas analyzer

Post by Gypsie » Tue Feb 19, 2008 9:47 pm

I am hoping to get some guidance about adjusting the
AFM without using a gas analyzer.

Can anyone explain how this is done. (Colin?..Wayne?...)
So it all started when I wanted to get better gas mileage....

vdubyah73
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Post by vdubyah73 » Wed Feb 20, 2008 5:38 am

Yes! A blow by blow account of how it's done would be sweet. All I know is that there is a gear that can be skipped a tooth or 2 and a nudge that can be made to the wiper and adjustments made somewhere according to what reaction the nudge produces. This should be made a tutorial stickie.

Bill
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IFBwax
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Post by IFBwax » Wed Feb 20, 2008 9:49 am

There is already a really good thread on this that Colin did with a guy who writes back every other month. Colin where is that thread?

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spiffy
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Post by spiffy » Wed Feb 20, 2008 10:48 am

Here is the multiple post version:

viewtopic.php?t=3223

Would be nice to have it with nice water color pictures on a page er two.



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Gypsie
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Post by Gypsie » Wed Feb 20, 2008 10:45 pm

Amskeptic wrote:
Your best field test for mixture, once it is running decently enough to not require babysitting at the AFM, is to simply nudge the wiper infinitesimally counterclockwise or clockwise with your chubby finger and listen to what happens:

if the idle goes UP counterclockwise, it is still too lean.
if the idle goes down counterclockwise, it is too rich.
if the idle goes UP clockwise it is too rich.
if the idle goes down clockwise it could be OK if it recovers the instant you let go.

If the wiper can move a 1/4" in either direction without materially affecting the engine revs, yer OK.


1. Mixture Screw Forensics: based on your information above, none has tried to hide a vacuum leak by running to that screw. This is good. Please take two and a half turns clockwise as our initial value on the mixture screw. This places us exactly in the middle of its possible adjustment range.

2. With a fully warm engine that has even had a chance to drive down the road for a good 20 minutes, re-check the wiper by the aforementioned little nudges, but see if you can read a tach-dwell meter while nudging. Try to get the most optimal rpms you can +/- 25 rpm. Even an analog meter can be very accurate if you can discern a needle on one side of a hash mark moving to the other side. You do not need to actually have the needle directly over a hash mark on the scale, you can just move your eyeballs to either side of the meter until you see the needle appear lined up. After you lock your eyeballs at whatever angle was required to have the needle lined up with a hash mark (note that I don't really care what the actual rpm is, we are just trying to catch a subtle change), gently move the wiper in either direction to catch the Very Most Optimal RPM you can. If you then tell me that you gained 25 RPM when you pushed the wiper counterclockwise, we will note, you and I, that the idle is slightly leanish but do nothing about it yet. If you find that you gained 25 rpm when you nudged the wiper clockwise, we will know that it is slightly richish. Move the wiper some more in each direction if you got no noticeable change in rpms. You WILL drop the revs in BOTH directions if you get ham-handed about it, that's OK too, just tell me if the distance-to-rev-drop favored CW or CCW.

As a preamble to our AFM adjustments, just lightly read the below to prime your mind to start working on the concepts subconsciously.

The AFM provides a complete matrix in the three possible adjustments provided:

A) the wiper hold-down screw inside that little oval slot I call the
Static Adjustment

B) the black cog with the teeth around its perimeter I call the
Dynamic Adjustment

C) the mixture screw I call the "trim adjustment" this week.

Between the three adjustments, we have the ability to affect the entire matrix, i.e. the mixture map.

Rich.
......
.........
.............
..................
.......................Lean

Low RPM/Load . . . . . . . . . . . High RPM/Load

Since this current php site code is stuck on "left margin" I can't draw you a graph. Use your imagination. Imagine a direct 45* line from lean/low up to rich/high. That is a simple fuel consumption curve in a perfect theoretical world.

Your static adjustment (A) will move that line up or down maintaining the perfect 45* angle at all times. If you adjust the wiper CCW by loosening the hold-down screw and easing it over a tooth, you move that line up towards rich. Low speed/load, high speed/load, doesn't matter, the engine's entire experience gets richer.

Your dynamic adjustment (B) changes the slope of the map. Imagine a nice curve up towards "richer sooner", or imagine a curve towards horizontal which is "leaner later." If you rotate the black plastic cog (by prying the chrome lockwire away from a tooth with your regular screwdriver tip and rotate the cog CCW (richer) or CW (leaner) you either unwind the spring coiled in inside, or wind it up still further.
This adjustment primarily affects the higher rpm/load.

If you play with this adjustment, there will be some "blowback" on the idle adjustment which you then take care of the mixture screw.

If nudging the needle subtly in either direction causes absolutely no change in rpms, you idle mixture is good. Verify with a tach-dwell meter that you get the same amount of movement in either direction before any change in rpms is noted. We would prefer that moving towards lean CW causes a sooner drop in rpm than towards rich CCW.

So now we have to check the high speed rpm. Bring engine to 2500 to 3000 rpm and hold it there with whtever mechanical means you can. A screwdriver expertly wedged is good. Sit and watch the engine hold that speed consistently. Now gently nudge the wiper barely 1/16" of an inch (maybe 1/4" if no noticeable change) CCW. Revs go up? Or do they go down? Now nudge CW 1/16" (or 1/4" if no change was noted). Revs go up? We want to know if any of your nudges brought revs up. . . Remove screwdriver when done. My site attorney told me to tell you that.
Colin

Okay.. I think this will help. sorry to create a redundant thread. If I have clipped something important out let me know. I like having this process in one thought stream. printable even.
So it all started when I wanted to get better gas mileage....

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Post by IFBwax » Wed Feb 20, 2008 10:57 pm

That is awesome! The key part is to use a screwdriver or something to hold your idle up there BUT NOT YOUR HAND... because you will psychologically, unwittingly move the throttle.

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Post by bus71 » Thu Feb 21, 2008 8:51 am

Thankyou! I have printed that and will use it to reclaim my lost mpg.

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Post by vdubyah73 » Sun Feb 24, 2008 5:32 am

Amskeptic wrote: So now we have to check the high speed rpm. Bring engine to 2500 to 3000 rpm and hold it there with whtever mechanical means you can. A screwdriver expertly wedged is good. Sit and watch the engine hold that speed consistently. Now gently nudge the wiper barely 1/16" of an inch (maybe 1/4" if no noticeable change) CCW. Revs go up? Or do they go down? Now nudge CW 1/16" (or 1/4" if no change was noted). Revs go up? We want to know if any of your nudges brought revs up. . . Remove screwdriver when done. My site attorney told me to tell you that.
Colin
So today I'm going to put my engine back in and give this a whirl. I have one question. What do you do when checking the high speed RPM if any of your nudges bring your RPM up?

Bill
1/20/2013 end of an error
never owned a gun. have fired a few.

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vwlover77
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Post by vwlover77 » Sun Feb 24, 2008 7:22 am

If your nudges in the CCW direction bring the revs up, the mixture is too lean. If the nudges in the CW direction bring the revs up, the mixture is too rich. Just like at idle.

Now, what I don't know is whether it is better to adjust the high rpm mixture using the toothed wheel or the wiper.
Don

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Post by vdubyah73 » Sun Feb 24, 2008 9:17 am

That right there is the crux of the biscuit. Probably won't be there today. Started working on it at 9, 25* out and rising, right now it is 11:00 temp is 32* and supposed to make it up to about 38*. Started with Bus on the ground, took rear wheels off for more wiggle room. Got the engine and tranny mated, tranny mid mounts next. Then rear bar, then, depending on my attitude wiring and plumbing. Tomorrow is supposed to be even warmer, I'll fire it up tomorrow afternoon. Keep your fingers crossed for me tomorrow.

Bill
1/20/2013 end of an error
never owned a gun. have fired a few.

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Amskeptic
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Post by Amskeptic » Sun Feb 24, 2008 3:43 pm

vwlover77 wrote:If your nudges in the CCW direction bring the revs up, the mixture is too lean. If the nudges in the CW direction bring the revs up, the mixture is too rich. Just like at idle.

Now, what I don't know is whether it is better to adjust the high rpm mixture using the toothed wheel or the wiper.
Bill, and Site Deputy Technical Editor, Don,

Don correctly answered your question, Bill. But the answer to which method of adjustment is a tricky one.

IF the high speed mixture is off in the same direction as the idle mixture, i.e. both are lean or both are rich, then you adjust the wiper. The wiper adjusts the entire fuel flow map. Be subtle.

IF the high speed mixture is opposite to the idle, then you have to adjust the black plastic cog.

If the idle mixture is perfect and the high speed mixture is off, then preset the mixture screw to 4 1/2 turns out from bottom and see which way the idle mixture screwed up, refer to above.

If idle mixture is perfect and the screw is at 4 1/2 turns from bottom, then adjust high speed mixture with black cog only and trim any resultant change in the idle mixture with the mixture screw.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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IFBwax
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Post by IFBwax » Sun Feb 24, 2008 5:51 pm

Colin.. please correct me if I'm wrong, but I found the wiper adjustment makes a huge change for just a tiny movement. You move that sucker two teeth and it's either way leaner or way richer. The black cog wheel seems much more subtle to me.. and that you need six teeth before you make a major difference... although you can fine tune it with one or two teeth.

In other words.. if you use the wiper.. expect your bus to really be changed quite significantly.

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Amskeptic
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Post by Amskeptic » Sun Feb 24, 2008 10:56 pm

IFBwax wrote: Colin.. please correct me if I'm wrong, but I found the wiper adjustment makes a huge change for just a tiny movement.
Hell yeah, that's why I said: "The wiper adjusts the entire fuel flow map. Be subtle."

IFBwax wrote: The black cog wheel seems much more subtle to me..
You CANNOT make a decision based on which seems easier to adjust with hooves. The wiper and the cog have specific functions. If the symptoms call for a wiper adjustment (the idle and the high rpm have the same mixture problem), then a wiper adjustment is what you are going to do. And I find that a 1/4 to 1/2 tooth is all I ever need to move that thing.

If you must adjust the slope of the mixture map (black cog), do NOT be lulled into thinking how "subtle" it seems to you, just because you do not get much of a reaction at idle. That thing gets into the act up in the higher rpm range where it melts exhaust valves. That is why the black cog is not primarily an idle mixture adjustment. It reacts to air flow, air flow happens when the throttle is opened. The black cog is the primary determinant of the high rpm mixture adjustment.

Do not monkey with the AFM adjustments unless you are intuitively familiar with you are doing.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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Gypsie
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Post by Gypsie » Mon Sep 15, 2008 10:05 am

Had to bump this back up cause I have a query.

I did the Colin Adjust Technique. I had it dialed in according to directions (with guidance from Spiffy and IFBWAX at Maupin).

The diagnosis was "too Lean" so I richened (???) 2 clicks on the 'dynamic' cog.

I ran for several months (Montana and back fully loaded). Temps low (300-350 on the freeway, with a few 400 spikes when climbing). 12 mpg!!

Accelerator had to be almost completely floored to maintain freeway speeds.

I still had 'fuelly' smell and black residue on the tailpipe.

I decided to lean back to start (2 clicks). Same temps, little less accelerator, 12.5 mpg.

Discussion at the Lab (beer fuelled of course) suggested a bit more 'leaning' to be in order.

Grabbed my huevos and roasaries and jumped into a four click lean out.

Freeway trip to the cabin (130 miles one way). Same temps. Loaded with trailer- 13.5 mpg, not loaded with trailer-15 mpg. Heading in the right direction

Now I barely have to depress the accelerator and she wants to creep up above 60.

Temp range: 55-60mph: 325-375 60-70mph: 325-400 (depending on incline).

Now I am curious, without analyzer is there anything I should be looking at to be sure I am not harming anything (other than head temps).

My figgering is as long as head temps don't spike I can lean out a bit more. I feel like I was runnning VERY rich.

The accelerator bit is odd. since the four-click lean out, barely depressed she wants to take off on the freeway. I was trying to keep at 55 to test the MPG wind resistance theory and was having difficulty keeping down to speed. She would creep up to 65-70 in a heartbeat. I kept having to lift my foot completely off to come back down to 55.

Is there some mechanical area to look at that would explain why the AFM theory is counter to these performance observations.

Curiouser and curiouser!

Also, what is the best substance to use to track down vacuum leaks.
So it all started when I wanted to get better gas mileage....

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IFBwax
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Post by IFBwax » Mon Sep 15, 2008 12:20 pm

Don't know the answer Gyp... wondering though.. have they changed the "blend" of gas yet.. back to Fall/Winter? Will they still do that?
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