as I understand it

at idle 


the afm has a bypass path that allows unmetered air to bypass the vane

this is controlled by a threaded plug of sorts and is designed to adjust the mixture at idle within a certain range

the bypass screws on the throttle bodies allow for a adjustable idle speed ....and because they are separate require synchronising  for a swiss sewing machine idle

the afm has a closed value of about 1.61 volts back to the efi computer (under seat ) which determines ...along with the water temperature and the thermistor (air temperature ) on the input of the afm  the relative duty cycle of the injectors (how much fuel per squirt )  this can be changed to make the extra fuel injection balance better with the air flow ...but tricky to do without some form of feedback - meter display

if you are getting a change in idle speed once warmed the idle mix is probably too lean ...and could be adjusted via the afm air bypass screw - slug



whilst cold , and additionally under speed (700 or so revs ) and increasing to  running temperature  the predetermined map for cold start conditions apply , along with an adjustable throttle opening device ie the choke lift bar via cable and electronic enrichment from the switch on the throttle bodies - choke lever

the start switch applies extra fuel above and beyond all the above .......and generally  a totally computer generated start sequence during start conditions  ...some have noted that there is a change in mix by pressing the start switch when running above the magic 700 or so revs

a good indication of fuel mix can be achieved by pressing the start button at temperature and noting the revs change ...or lack of  and to be read into the designed carbon emissions standards and adjusting techniques.
 

hope that helps a little

Here is an idea of what it sounds like, however a lot of the deep sound gets lost. It sounds way better in person.

Kaptain Holister wrote:

KafeRacer wrote:Does anyone know how an L-Jetronic system is affected by the water temp sensor?
There are 3 stages the L-Jet goes thru while warming up.
Cold Start Enrichment: Only when the starter button is pressed the ECU increases the injection time considerably after checking the coolant temp. This is to compensate for fuel condensing in the intake chambers and cylinders and not vapourising completely prior to any ignition. If temps are very low ie <0°c, injection times can be doubled by the ECU.
After Start Enrichment: When the starter button is released and the motor is running (>720rpm), The ECU goes into After Start Enrichment mode for around 30 secs. The ecu monitors the coolant temp and increases injection times by 30 to 60%.
Warmup: At this point the ECU monitors air flow and temp and adjusts fuel injection times so as to maintain idle untill the engine reaches operating temperature and the ECU produces a base injection time.

As I have installed a wide-band O2 sensor I can monitor the AFR.  The way it is configured now is as follows:

Bike Idles at 1070 shortly after starting and warm enough to not need choke - AFR hovers at 14.
Bike continues to warm up idle slowly increases to about 1250 after 10 minutes - AFR hovers at 14.
Note:  If I press the start button, it riches the mixture (as notes many places on the forum)  With the starter button pressed the AFR richens to about 12, release button and it goes back to 14.
AFAIK the ECU ignores any further signals from the starter button once the engine is running over 720rpm.

After the bike warms up further there is a distinctive point where idle shoots up from 1250 to 1600, and AFR richens from 14, down to 11.8.  Note: Once this occurs, pressing the starter button no longer richens the AFR. At this point pressing the starter button has no affect on AFR.

I assume this is normal, and just a change in the fuel map after the bikes water temp reaches a certain point.

I am also assuming that if I adjust the AFR to be leaner at operating temp, it will be quite lean before the L-Jet changes to its operating fuel map.  Should I be concerned?  I am assuming not, and that running lean during warm-up will simply result in reaching operating temp faster?
I would guess that your #415 injectors would be producing a reasonably rich mix at 3.5bar so leaning it out would be good but running 'lean' would not be ideal.

I also notice that once the bike is at operating temp the spring tension on the air flow meter has virtually no affect on the AFR at idle. Does the L-jet not look at the air flow meter when the throttle is closed? And simply apply only a fixed amount of fuel?

Just looking for thoughts.

Great, thanks for the info.  I like to have an understanding of how the ECU works as it can aid in tuning and troubleshooting.  I do have the bike running well now.

Cheers.

charlie99 wrote:as I understand it

at idle 


the afm has a bypass path that allows unmetered air to bypass the vane

this is controlled by a threaded plug of sorts and is designed to adjust the mixture at idle within a certain range

the bypass screws on the throttle bodies allow for a adjustable idle speed ....and because they are separate require synchronising  for a swiss sewing machine idle

the afm has a closed value of about 1.61 volts back to the efi computer (under seat ) which determines ...along with the water temperature and the thermistor (air temperature ) on the input of the afm  the relative duty cycle of the injectors (how much fuel per squirt )  this can be changed to make the extra fuel injection balance better with the air flow ...but tricky to do without some form of feedback - meter display

if you are getting a change in idle speed once warmed the idle mix is probably too lean ...and could be adjusted via the afm air bypass screw - slug



whilst cold , and additionally under speed (700 or so revs ) and increasing to  running temperature  the predetermined map for cold start conditions apply , along with an adjustable throttle opening device ie the choke lift bar via cable and electronic enrichment from the switch on the throttle bodies - choke lever

the start switch applies extra fuel above and beyond all the above .......and generally  a totally computer generated start sequence during start conditions  ...some have noted that there is a change in mix by pressing the start switch when running above the magic 700 or so revs

a good indication of fuel mix can be achieved by pressing the start button at temperature and noting the revs change ...or lack of  and to be read into the designed carbon emissions standards and adjusting techniques.
 

hope that helps a little

Thanks for the response and all the great info, I have adjusted the idle air bypass as well as spring tension on the vane.  I also balance the TB's using the procedure I found elsewhere on this forum.

Cheers.

Well, after reading some posts about the throttle position sensor, which on the 2v TB is only used to detect full open and full closed throttle positions, I decided to disconnect it to see if the bike would run smoother in stop and go traffic by avoiding having the ECU cut the fuel under 2k RPM. I am absolutely amazed at the difference it made, no placebo effect here, it is night and day better.  After removing home from work I promptly removed the sensor entirely.

Cheers.

I wouldn't remove it entirely as the L-Jetronic can run very lean at high speed which is why the rich run was included in the system. Seems to me to be taking a chance on smoking a set of pistons at a very inconvenient time.

When I went to the 35mm TBs on my K100, I never got round to fabbing an adapter to allow the earlier TPS to fit the newer TB's base. I simply left the clip lead disconnected, and did notice it transitioned more smoothly in stop 'n' go traffic. But I was always slightly concerned I was not covering my arse in a high speed, hard acceleration runs due to leanness. It's been several years now. I wonder what those piston tops look like...

I have my AFR guage mounted on the dash, I can monitor the mixture, I will keep an eye on the number, but what I noticed today seemed reasonable.

Also, if I detonate an engine, I will have a good excuse to find a K12 engine for the beast.