Still tinkering with my new NOS but idle is very inconsistent. Seems like (way?) too rich but without A/F bung it tester not sure which way to turn the adjuster screw to lean. Haynes says just “adjust” but not VW or CCW.
Turn in Clockwise to lean?
Click to view attachment
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Wish I had a CO-A/F sample port.

The CO screw in the AFM is a bypass screw. So closing it (clockwise) will increase the CO, and opening (CCW) will decrease the CO.

What it does is to allow more air to bypass the vane air meter door when the screw is turned counter-clockwise. So the door does not deflect as much, and the CO goes down.

Hope that helps.

OK, thanks Clay. CW (in) goes richer; CCW (out) goes leaner.
It's almost all the way in now, so might have to turn the internal tooted wheel (CCW for richer) but not until I get the sample port bung to measure what I have.
AARGH!!

I recommend that you don't mess with the internals of the AFM. But if you do, don't change the spring tension by turning the toothed wheel. You can let it slip and unwind the spring, which takes a special tool to recalibrate.


There is a small screw in the middle of the AFM. If you loosen it you can change your wiper contact position to adjust the mixture. Move it only a tiny bit at a time, and make sure the fuel shutoff contact still works after you move it. There are teeth on the outside you can use with a screwdriver blade to adjust it.

@StarBear

i'd take @ClayPerrine 's advice on the old screwing around with the AFM too much.


you might have opened an interesting can of worms.
going back to your original thread where you investigated interior of your original AFM
and the NOS one you are now installing.

http://www.914world.com/bbs2/index.php?sho...65536&st=20

thinking about the wiper board part numbers inside those two AFMs.
i guessing the NOS one has maybe got the later 75 wiper board or an adaption of it given that the part number in the last three letters is a superceding number higher up. i would have to know what the sweeper board part number is in a 75 to know for sure.
but maybe thats what bosch did? adapted parts from the 75 and wired it such that it could be adapted to the earlier 6 pin plug outlet?

there are some subtle differences to the 74 versus 75.
not quite the same settings anyway.
CO much lower in 75. and power curves are a little different.
some of that is going to be down to the ECU but maybe its also in the AFM to some extent. i dunno enough about this stuff. but its a little inrigueing that the NOS 6 pin AFM you have with the correct part # for 74 has that later higher number wiper board in it.


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when you get it set up to your satisfaction re idle it will be interesting to hear your report on how it drives afterwards and is there any subtle or discernable difference in the car.
i mean we are talking fractions of horsepower in a frighteningly powerful 72 hp fire breathing L jet. but the torque curves are discernably different as is the power off idle. funny stuff.

Oh, just saw his advice. Thanks for the notification.
Have started tinkering with it, with mixed and contradictory results - trying to not lean while also increasing spring tension.

i just realised those power curves are different measurements.
SAE v DIN. so probably does match from 74 to 75 in terms of power off idle and max power, but the curves are different on the way to the top end and max power and max torque do occur at different rev points. hmmm.

Interesting information; is the ‘75 L-Jet capable of cruising at 4K rpm?

good question. maybe in germany on the autobahn its meant to.
4k probably is like sitting at 90-100? i'd say it can and its meant to.
the original theory of the bug engine is cruise speed = flat out speed.
engine was kind of engineered to be that way too.
without blowing up. sort of self governed due to exhaust and head design.
type 4 probably not too far from that idea though way better heads on a type 4 in terms of exhaust flow etc.

in practical land of north antarctica speed limits hold me to 65mph.
which is usually 2800-3000.
you are just not meant to lug them at lower revs, thats when the trouble happens with overheating.

i did once cruise my 74 1,8 at about 90-95 for maybe it was 20 minutes, to half an hour.
in western australia about 30 years ago north of perth in the flat desert there. can't remember the revs. but i do remember the speed. it felt ok and comfortable getting there and staying there. it did not want to go much faster comfortably, also the nose started to lift at about 95. so i reckon new, they could cruise up there near 4K and at 90 all day long on the autobahn and were meant to do it.

@clayperrine
Here’s the pic of part numbers on the plastic cap.

Click to view attachment

A few years ago whilst messing around with the AFM ( wasn’t delivering enough fuel) during the process of easing the spring tension on the toothed wheel to allow for a richer mix under load, I inadvertently let the wheel get away... Sproing!

I figured I totaled the thing, but ended up rewinding it and readjusting it according to the A/F meter. Got it back together but really startled me when it let go...

Anyway, there’s a good tutorial on Itinerant Air IIRC, I followed that to get it to the point where it’s very good, with the exception of cold starts, where I have to slightly feather the throttle for up to 30 seconds or so. It will idle at that time (since installing a 123) but it’s low, around 500rpm. So I just give it a little pedal.

I’ve checked the AAR valve, it seems to function as it should, but this is a 2056 with a 9550 cam so that may have something to do with it

Here ya go

http://www.itinerant-air-cooled.com/viewtopic.php?t=7761

screw it in to richen, usually AFC L jetronic cars do not ever run rich unless the air flow meter flap is sticking or wildly misadjusted, the head temp sensor is bac, or the fuel pressure is out of sight due to a return line blockage

Yep, heard of that happening; being REAL careful!
Thanks for the link; will check it out. Have also ordered the Bosch book (blue) on L-Jet FI management.
I WILL get back on the road again; just not in time for this weekend’s NE Gathering.

Thanks, George. I’ve assumed CHT and fuel pressure is ok as it was running fine until the new AFM. Will check them just to be sure.

Don't forget that the stock 75-76 exhaust is just horrible. I'm betting that most or all of the detectable difference in power is due to that. It really is bad, going against pretty much every rule of how to get an exhaust to make power.

--DD

when you say the idle is inconsistent what is it doing exactly?
hunting up and down from approx 900 and then back down again and then up again?
(not talking vac leaks either - know it won't be that on your car).

mine does this intermittantly. like once every 6 months.
did it again yesterday. fiddled and shook everything hose and throttle related and farted around in the engine bay.
wouldn't stop doing it.
switched it off. left it for 10 minutes. went back started it with a little more difficulty than usual. and then gave it a good cleanout rev or three. and the problem went away again. idled rock steady. had not touched a thing setting wise. last time it did this was i think last year. it was bloody cold here yesterday. weird. i think its some kind of fuel supply problem. i was blaming the fuel pump. but i am wondering if the AFM is bouncing around on the fuel pump contact end of things at idle or even sticking slightly on a cold day or the TPS wasn't quite switching to idle position.
the mystery of 50 year old components.
anyway, not getting too fussed about it, but its a weird little gremlin that surfaces every now and then.

Have read the info in that link several times - it’s fantastic! Great info in non technician language. I think I have it and will start digging into it tomorrow. Also got a blue Bosch FI management book ; not very helpful for this venture.

@wonkipop
Just wonky in general. Sticks at 2000 at slow deceleration and sometimes drops to shut off before kicking back up to stable. Bucks at 3000 momentarily at times. Not sure if too rich or too lean but that link info tells exactly what to do and how.
Really have to get that sample port bung once I get it closer to dialed in.

ah yeah
the drops to shut off before kicking back up again is what mine was doing yesterday.

which is why my speculation on when this happens in mine is it has something to do with fuel. i know its not vac leaks. but thats not helping you necessarily.
i was thinking about what mine was doing yesterday and wondering why, and why this day and not other days. different problem i suspect. but interesting the way it would almost die and then burst back into life and then die again on repeat.
the joys of the L jet.

and like i say it went away. and it wasn't affected at throttle open. no problems there.
it was like it was hovering around in there turning the fuel pump on and off at the bottom end of flap movement. either that or my fuel supply was actually being interrupted somewhere and it cleared itself.

@Porschef
Problem solved!!! New 6-pin second generation air box now dialed in, much thanks to your link info. What a great write up - even the Bosch FI Management book didn’t come close to helping.
Turns out, there are 3 A/F settings. Will wait until getting a sample port bung to fine tune with proper analyzer. No spring “sproing”!
Vroom vroom!

can you document what you did?
could be handy if i ever have to try and pick up a replacement AFM.
you never know with an L jet. classic.

@StarBear find yourself a emissions testing shop that has a 4 or 5 gas analyzer and ask if they can dial in the idle CO for you. No test port required as 74 does not have a catalytic converter just sample probe in the tail pipe. Set to either spec CO per the VECI. Unless you are trying to dial in a near stoichiometric air fuel ratio during cruise. I'm running at 3% idle CO to keep things a little cooler. Hooked mine up to a 5 gas analyzer to dial in my CO setting. If I didn't increase the CO setting with the Pertronix ignition I have, I would still pass emissions testing even though my 914 is exempt here in CA when I was taking an engine performance course (smog testing/diagnosis) towards my AS degree in Automotive Technolgy. The link posted is the one I used to learn how to reposition the fuel pump contact arm that someone adjusted to make the pump run all the time with the key on my guess to alleviate the vapor lock issue.

Congratulations, and thanks for sharing your experience working on the AFM. It literally is a black box for most of us. A while back I pulled my L-Jet 1979 Super Beetle out of long term (16+ years) storage and went through all sorts of fun trying to get it to pass the California smog check. In the end what worked was screwing up the courage to open up the AFM and adjust it. It was a trip down a rabbit hole, but I figured everything I learned would be helpful in any future dealings with my 1975 914 1.8. Porschef already provided the link to one of the main information sources both you and I used. Sorry to be chiming in to late to be helpful to you, but because I know others may stumble across this thread when they are trying to find information on the AFM I'll include a link to two other threads that helped me out. Obviously these relate to the AFM on a Super Beetle/Bus but they are applicable. They are both from the Samba.

This one might not seem obvious at first since it started out to be about suspension issues, but go to the post near the end that was put up on March 10th at 11:58am. There are some helpful pictures as well as a method for adjusting while AFM while the engine is running.
https://www.thesamba.com/vw/forum/viewtopic...77&start=80

Less helpful (at least for me) but there are some good bits of information about AFM settings in this thread: https://www.thesamba.com/vw/forum/viewtopic...afm&start=0

Porschef already gave this link earlier in this thread, but I'll include it here just for the sake of completeness. This was the most helpful. https://itinerant-air-cooled.com//viewtopic.php?t=7761

Finally, if you are bored, or that gummy is starting to kick in and you have nothing better to do, here is the thread with my journey to get my SB to pass the CA smog test. https://www.thesamba.com/vw/forum/viewtopic...sc&start=40

Idle screw last steve-o. The car will tell you when it’s happy. All the way in and then come out until idle peaks and then back in a 1/4 will put you in the ball park.

Just followed the instructions in the link - very carefully. It’s only applicable to the second generation 6-pin and I supposed the 7-pin units as the first gen 6-pin units don’t have the tension spring for dynamic adjustment.
Will relook at my first gen unit to compare and see what is applicable.

@StarBear - is this the dynamic adjustment tension spring that is on the later 6 pin replacement AFM?

Click to view attachment

EDITED: No. The “static” adjustment is the center screw and small toothed arc. The dynamic adjustment is the "W" tension spring. Then , there’s the small adjustment screw on the air box for fine tuning.
The static apparently affects the entire fuel map. The dynamic affects more the mid and upper map.
May try to post new annotated pic tomorrow. Fireworks tonight!!!

ah yes the 4th of july. happy independence day.
its the 5th here, we are ahead of our own time.

Great stuff! Glad it was able to help you out; I can’t remember how I found/stumbled on/was told about that site but it helped me immensely, written and illustrated in such a way even I could understand…

I had been messing with it while trying to eliminate some pinging under load, after tuning up the stock distributor and adjusting timing; something that has all been eliminated with the 123. Static A/F shows somewhere around 12.7-13 at steady cruise, dropping down to 11.5 or so under load. No pinging at all. Head temps vary according to ambient temperature but typically run around 340-350° most days. An auxiliary oil cooler has kept any heat soaking at bay.

I’m curious about your cold start performance. My cold idle is low, despite what seems to be a perfectly functional AAR

Congratulations

@wonkipop and other 1.8 L-Jeters:
Here's the side-by-side comparison of the 6-pin first generation and the 6-pin second generation.
I'm not sure if dynamic adjustment can be made on the first generation unit, or if it can, there simply is no tension spring to "lock" it into place?

Click to view attachment

My cold start was fine (slightly high for 1-2 minutes then settled down) before the AFM issues. Now with the new box it starts and stays at the target (but then, lately I've not had exactly what one would call a "cold" start, at 70F plus in the morning).
Checked out the AAR and OK, so might still have to tweak the A/F at idle once I'm able to measure it.

For those die-hards, I've made that handy Ljet AFM adjustment link writeup into a PDF. Sharpened and adjusted some of the figures to make them easier to read for us "more mature" (older) folks.
Click to view attachment

@StarBear thanks mate.
downloaded and filed away.

if i ever replace dinosaur jnr in the jaffa.

yeah i have a cold start low idle.
and i checked out the AAV and it works well. i think. was two or three years ago.
and i have a adam in the garden of creation AFR i am too gutless to open up.
so.........i dunno but its warm after about 2 minutes its fine.
so i'm not going to go full @StarBear yet.
besides i dont have one of his seriously updated NOS improved 6 pin devices.

so like you i am stuck with the pathetic cold start idle.
ah well. its half a century old.

you guys don't forget that my AAV tested good when I was investigating my cold start issues. But performance was still not good enough as revealed when I replaced it with a standard motor products substitute and immediately got fantastic cold idle performance.

Get a wide band to be sure. Sounds like a part load issue though.

Van; what do you mean by “a standard motor products substitute”? A brand name?

Yeah you guys forgot the thread where I went through all this a year ago. Stand by let my dig it up

This is the one I bought:
https://www.summitracing.com/parts/smp-ac358

Same Bosch body, but internal disc is different. Bigger engine in the old M5 so it flows more air. But closes at the same rate as any other.

Here’s the post:
http://www.914world.com/bbs2/index.php?s=&...t&p=2988976

Thanks! Missed your prior post somehow.

@wonkipop
@L-Jet914
@Van B
Ok, so I got the O2 sensor plug port installed and got the new 2nd gen 6-pin AFM dialed in at 13 A/F at 1000 rpm idle and 14.4 A/F at 3000 rpm no load. Runs great!
Have ordered my own Innovate analyzer and will check A/F at 3500 rpm and load (typical driving). Shooting for maybe 13 A/F.
Once with the new analyzer will try 13.5 A/F at idle.
Question: At what A/F ratios do you guys run?

13.5 part throttle so that full throttle enrichment gets me around that magic 12.5:1

However, attempting to achieve those numbers are a good reminder that as good as AFM injection was for its time, it is still an antique lol…

To be honest I have no idea what my AF ratio is when I am driving as I do not have a AF sensor plumbed into my exhaust system. I would have to run a mock smog on machine to see where I stand emissions wise haha and then do a lambda calculation based off the numbers I get.

From the factory L-Jet was set to 3% CO. If you are at 13.5 you are a little lean at idle. Not enough to notice, but not exactly where the factory set it up.

To set it like the factory did, you need a CO meter, or a chart to convert the AFM to
CO.


Here is a chart for you.

Perfect, Clay! That’s really helpful. I’m at 13 now so can still tweak it a bit once the Innovate arrives.