TheSamba.com :: View topic - L- Jetronic FI AFM questions

Mon Aug 25, 2014 3:19 pm

hello all!

So in the ongoing effort to restore my baby to her pre-fire self, I've pretty much got her running.

The idle is rough and I've been without any good help on this FI system. The top part of the AFM containing the idle mixture screw (i think) and the wiper is exposed in my bus, and when i googled and idle set screw, that popped up.
With no one to tell me I was wrong, I adjusted it thinking i was setting the idle itself, and played with the timing too; getting it to 7.5 BTDC, where it's supposed to be. Now my bus is slow and powerless, shifting hard and in the wrong places.
I need to know where that idle mix is supposed to be set stock, and what tools I will need to get this done, so I can adjust the ACTUAL idle set screw and maybe reset the timing.

Mon Aug 25, 2014 3:27 pm

The idle by-pass screw on the AFM should be in about the middle of its range. I think that is about 7 half turns from tight.

You set the idle speed using the"big screw" on the throttle body.

Does the inside of your AFM look like this (note the white dot above the "e' in screw)...

Mon Aug 25, 2014 3:42 pm

Randy in Maine wrote: The idle by-pass screw on the AFM should be in about the middle of its range. I think that is about 7 half turns from tight.

You set the idle speed using the"big screw" on the throttle body.

Does the inside of your AFM look like this (note the white dot above the "e' in screw)...

Exactly the same, and this is actually the picture I looked at (should've clicked the link it was pertaining to, silly me). I have sinced been corrected by my dad about the idle set screw.

Randy, you're the badass of the day in my world! thank you.

Mon Aug 25, 2014 4:26 pm

If you adjusted the wiper and/or the idle bypass you probably need to get the whole thing adjusted by an AC shop with a gas analyzer.

The only thing you can adjust at home without a gas analyzer (or aftermarket O2 meter) is the idle screw to adjust idle RPM (using a tach/dwell meter).

Without the means to measure the AFR and/or CO you have no idea what you're doing with the other two. You might make the engine run real good by trial and error...but it might be cooking itself in the process.

I've found an installed O2 meter (LM-2 in my case) to be very useful for tuning and monitoring the FI type-4.

Wed Aug 27, 2014 12:53 pm

amskeptic has a good writeup about this.

The long and short of it is, you can adjust your idle mixture pretty accurately by nudging the wiper arm left or right at idle (just use your finger to nudge it one way or the other while it's running and with the top off the AFM.) If the idle speed increases when you move the wiper left then it's too lean. If the idle speed increases when you move the wiper right then it's too rich. Adjust accordingly, turning the screw clockwise is more rich. You want it just on the edge of lean. If you have to turn the screw all the way in it means you have a vacuum leak.

If you messed with the idle mixture and the timing, and it runs like crap, my guess is the timing is to blame. The idle mixture really doesn't have a large effect at normal running RPM.

Try setting your timing to 28 BTDC at 3000+ RPM with the hose to the distributor pulled off and plugged. That should put you where you need to me. Setting the timing at idle is the Bentley way but a lot of people feel it's not as good of a method. Setting it purely based on the mechanical advance at speed makes sure the timing is where it's supposed to be under heavy load, which is when it counts.

Also, you should have a cover on your AFM. It's not good to leave it exposed to dust and debris.

Sun Nov 16, 2014 10:36 pm

Guys, thanks for the help. I still need to fine tune the system, but I got it idling just fine now. I noticed that my Intake elbow to aux. air regulator hose was leaking at the S boot junction. The hose is a bit loose at the ends; ideally I'd get a replacement, but in the meantime I'll clamp it on both ends and hope that does the trick.

Thanks again guys!!