911 2.7 S CIS hex mixture screw help

[tangerine69s]

Hello,

Some time ago I had a problem with starting our 1977 911 2.7S that resulted to be the fuel pump but in between we messed up the 3mm hex allen screw that adjusts the mixture and now we don't know where to start.

The system is in perfect condition, vacuum, points, ignition... fuel arrives to injectors and sprays correctly.

The thing is that the car don't start as we think that the mixture screw is COMPLETELY badly adjusted.

I understand that clockwise is to enrich and counterclocwise to lean mixture but how do we start from scratch?

THANKS!

Josep

[T77911S]

make sure the CSV is working properly first.
its also a good idea to know what the control pressures are before but since you have already diddled the mixture we can move on.
the other thing is the 77 has a vacuum controlled warm up regulator (WUR),. make sure it has vacuum at idle, and again the CP needs to be checked with and without vacuum to the WUR,
the WUR will drop the CP .8bar with no vacuum thus making it richer.
you need to know if this works.

if you have no idea where the mixture is I would, with FP's running (you can do this by removing the connector on the top rear of the AFM and turning the key on), turn the mixture CW until the injectors start to spray, then CCW until they stop.
start it.
let it warm up.
move the sensor plate up and down to see if that makes it run better.
up means it needs to be richer
down = leaner.

another method is to have someone start it while lifting up or pushing down on the plate to get it running, then adjust the mixture so you don't have to hold the sensor plate.
then do final adjustments,

here is how I set mine on my 77.
with it idling I would adjust it rich until the RPM would drop.
then back off until it came back up
blip the throttle. if the RPM's dip down then come back up when you let off, it is too rich,.
if it surges while idling you are too rich.
keep adjusting leaner until there is no dip and no surge.
yea people it says final adjustments need to be in the CW direction. once you note the angle of the allen you can go CCW then back CW if you want, I tried just going CCW and never noticed anything.
I always adjusted it for right on the edge of too rich.
when I did connect my LM and check the mixture it was dead on.

one last thing. its not good to let it idle for a long time, you will get false mixture settings so you will have to drive it and make some fine tuning.
just try to get it on the edge of too rich.
also verify timing before you start.

[rwest]

There is a factory procedure for setting it at a baseline; hopefully someone can clarify it, since my memory might be shaky.

You first take the injectors and put them in jars and then you jumper the fuel pump and turn the mixture either up or down until the injectors just spray and then back off the screws until they just stop- and here's where I'm a bit foggy, you then turn it like a half turn richer, then that gives you a starting point to adjust for AFR.

please, someone verify my info, or if not, I can look it up in my manual later.

[gazzerr]

Yep CIS manual says turn it CW until they just barely eject then back it off CCW 1/2 a turn. That's your baseline. You can hear them squeal when they start to eject.

[tangerine69s]

The weird thing is that the hex allen 3mm bolt does not adjust the injector flow.

I have this bolt underneath the plate, inside the air box, I haven't touched this as it seems that is correctly adjusted. No flow when power on until ignition, then gas flows through the injector.


Adjusting allen bolt does not seem to make any difference. Engine does not want to start.

[al lkosmal]

you should not get flow through the injectors by just turning the ignition on.....injectors should not flow until the air flow paddle is lifted.