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Old 03-10-2013, 01:36 AM   #1
fata moutra OP
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Joined: Jun 2007
Oddometer: 20
k75 running rich

I did not have any experience with the K series until a friend of mine asked me to sort out his K75 that was running very rich. When you blip the throttle thick black comes out of the exhaust, and if you open the throttle very fast it tends to stall. I have done some reading on the matter and checked the following

injector resistance OK
cleaned injectors and checked injector spray and flow
ground connection if injectors OK
communication between injectors and jetronic OK
TPS OK
comm TPS-Jetronic OK
balanced the throttle bodies bypass screws
fuel pressure OK
crankcase breather tube fixed (was torn)
cleaned the air flow meter potentiometer and its ''door'' it seems to move freely
Changed battery
air filter OK
temperature sensor OK

Nothing worked, i am back at the beginning. The thing is that as i have read the air flow meter and the Jetronic are considered to be bulletproof. So if they are not the source of the problem what else could it be? Unfortunately i dont have a second bike handy to check its Jetronic and MAF meter.

i would very much appreciate any help on this
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Old 03-10-2013, 03:43 AM   #2
damurph
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I am not much help but If you had a location for the work being done perhaps somebody local might be able to help.
There could be someone living around the block to change out parts for diagnosis purposes.
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Old 03-10-2013, 05:11 AM   #3
fata moutra OP
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unfortunately i am in patras greece so.. not many adv riders near me :)
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Old 03-10-2013, 06:03 AM   #4
duck
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Quote:
Originally Posted by fata moutra View Post
I did not have any experience with the K series until a friend of mine asked me to sort out his K75 that was running very rich. When you blip the throttle thick black comes out of the exhaust, and if you open the throttle very fast it tends to stall. I have done some reading on the matter and checked the following
Model year and mileage? Does this happen when warmed up or only when engine is relatively cold? Did this happen suddenly or gradually get worse?

Quote:
cleaned injectors and checked injector spray and flow
Did you have the FIs professionally cleaned?


Quote:
temperature sensor OK
What does this mean? How did you test it?

Quote:
Nothing worked, i am back at the beginning. The thing is that as i have read the air flow meter and the Jetronic are considered to be bulletproof.
The spring in the MAF can get old with high miles. The L-Jetronics are relatively "bulletproof" but not 100% immune to failure.

Have you checked the valve clearances? (When the engine is cold.)
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Old 03-10-2013, 07:58 AM   #5
fata moutra OP
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1) i think it is a 1988 k75c like this one . The problem is evident both cold and hot.
http://motoprofi.com/bikephoto/4023/...5_c_1988_2.jpg
2) about the total kms i am not sure because the speedo doesnt work. it is propably 100000 km
3) the injectors were cleaned with an ultrasound cleaning device and then checked for even flow and spray pattern by me at the technical school that i am working. I think it is a straightforward task, although i forgot to backflush them anyway the spray pattern imroved after the cleaning and the one injector that was spraying less than the others was ok after the cleaning procedure
4) i measured the temperature sensor via the socket that connects to the jetronic through pin #10 and ground using these values that i found on an other site
0° - 5K5
20° - 2K5
40° - 1K25
60° - 600R
80° - 320R
100° - 1909R
http://www.i-bmw.com/showthread.php?t=17210
Next thing is to try to ''adjust'' the MAF spring....
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Old 03-10-2013, 08:52 AM   #6
duck
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If you leave one of the early ones (about 88 and older) on the side stand for any period of time then oil will seep past the rings into the combustion chamber. This can cause them to be very smokey for a while until it all gets burned off.

If that's causing the issue then:

1) Use the center stand.

2) Once the bike is turned off, tilt it to the right for 10-15 seconds to let the oil behind the pistons drain back into the sump from behind the pistons.
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Old 03-10-2013, 09:05 AM   #7
fata moutra OP
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as an owner af a gs i know all about oil seeping in the cylinder :)
the bike is parked on the center stand
it is black smoke not white so it is not oil . It smells of unburnt gasoline afterall
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Old 03-10-2013, 09:42 AM   #8
duck
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Have you pulled the spark plugs to inspect them?

BTW: The spark plug leads on K bikes need to be very solidly attached. Pull off the spark plug cover and wiggle the leads. If there's any wiggle in them at all then they are not on properly. To make sure they're all of the way on: Grab the tab on the spark plug lead in one hand with some pliers and hit the pliers with your other hand to get them fully on.
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Old 03-10-2013, 10:20 AM   #9
larryboy
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Played with a K100 one time, that stupid speed density door thing was stuck. TPS demands fuel and dumps it in, door doesn't open and the engine doesn't get air. Horrible stone age system.
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Old 03-10-2013, 10:39 AM   #10
fata moutra OP
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the plugs are all black from the rich mixture but they have good spark and the caps sit firmly on the plugs.
The air flow meter door seems to move freely. Only thing is when i removed the airbox and connected the air flow meter directly to the intake the bike could not idle unless the throttle was a little open or the choke lever pulled
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