Need Help 1990 K75RT 48K

Bike would not start. History 3 weeks ago bike failed to start one time. Then ran normal for two weeks. Last time it ran normal I started the bike and pulled it out of the garage and it died.

I have cleaned some connections, have spark and fuel pump operates, have unplugged and replugged the brain, ignition module, mass air sensor and have replaced the fuel filter. Air filter is a K&N that came on the bike when I got it last year. Appears to be clean and normal.

Current state: Bike will start and run at approximately 500rpm. Normal idle was 1100rpm prior As soon as I attempt to roll on any throttle it dies.

So fire away and give me some good ideas for a rainy day repair Tuesday the
25th. Thanks in advance for your help.

Mike hankinson Hudsonville MI

I recently had this same problem on a 1987 K75. Exact symptoms. The culprit? Mass air flow sensor was not in the boot. Open the flap with your finger about half way and see if the bike will take gass.

Ralph Sims

Thats a good idea.

Also how is the fuel filter. also the fuel pump sock? Fuel reg etc:

Air Mass Sensor What Next

Ralph, yes, by opening the mass air sensor with a screwdriver I can run the bike up to higher rpm and sounds good. Now how did your problem end up? Did you
have to replace the mass air sensor? I had checked that to see if it was stuck before and it moved so I figured it was okay. When you said yours was not in the boot? Exactly what did that mean? Appreciate the feedback.

I mentioned in the earlier post that I had changed the fuel filter and no change at all there. I am getting good fuel flow so it is definitely the air program.

Sure appreciate the feedback.

Mike Hankinson Hudsonville MI

MichiganMike said:

Ralph, yes, by opening the mass air sensor with a screwdriver I can run the bike up to higher rpm and sounds good. Now how did your problem end up? Did you
have to replace the mass air sensor? I had checked that to see if it was stuck before and it moved so I figured it was okay. When you said yours was not in the boot? Exactly what did that mean? Appreciate the feedback.

I mentioned in the earlier post that I had changed the fuel filter and no change at all there. I am getting good fuel flow so it is definitely the air program.

Sure appreciate the feedback.

Mike Hankinson Hudsonville MI

Click to expand...

I bought the bike non running for a song. The PO parked the bike and it never ran again. John Diaz had the MAF sensor idea.

The bike had new coolant hoses, and I assume that whoever installed them removed the air box. They did not install the boot into the airbox correctly and I supose the MAF wiggled out of the boot. I put it all back together correctly and it has run fine.

With the MAF out of the boot the flapper could not open. If your MAF is installed correctly and the flaper doesn't move from the air drawn into the intake, I'd say you have a stuck flaper.

Since the bike runs with manually moving the flaper, maybe you could lubricate it with something. I have seen mass airflow sensor cleaning spray at auto parts stores. I have never used it, though.

Ralph Sims

MAS & Flapper

Tomorrow morning I will get back in there and see if something is loose and or not working as it should be. I just opened the flapper and it ran perfect. So will see what the light of day brings tomorrow. Have had a long day today so will wait till I can concentrate and make sure it is done right. Thanks I sure appreciate the feedback on this problem.

Mike Hankinson Hudsonville MI

Wed Progress??

This morning I checked the contacts and plug for the MAS again and put new stock BMW Air Filter in. Put things back together after checking all I could check on the MAS. Bike still would just start and run at approx. 500 rpm. SO, Ordered a part from BeemerBoneyard that should be here on Friday afternoon UPS. Then I can see what happens next. Still riding the trusty Airhead GS until Friday.

Mike Hankinson Hudsonville MI

Replacement MAS 90 K75

UPS Delivered my part from BeemerBoneyard today on schedule. Installed the
new part (Mass Air Flow Sensor) in the top half of the air box. Made all connections and no change.

Bike will still start at 1/2 notch on the choke, idle at approx 4 to 5 hundred rpm and as soon as the throttle is moved the engine dies.

As mentioned earlier, with manual opening of the flap in the MAS the bike would
run up to higher rpm.

Need help above my manuals here to know where to go next. TIA.

Mike Hankinson Hudsonville MI

Possibilities to check:

1. Fuel pressure
2. Injectors
3. Strange glitch in the throttle position switch
4. LJetronic

LJetronic Test

Do most dealers have the capability to test a LJetronic out of the bike to see if it is working or am I dreaming? I assume the only other way would be to have a unit out of a similar bike to plug in and try at home. At this point looks like the R100GS will have to bring me down to Falling Leaf next week. Need to get to my favorite rally of the year.

Mike Hankinson Hudsonville MI

Final Result

The K75 runs again. I followed another thread on the Forum on a K100 with the same symptoms that I had. One of the replies on that thread provided me with an answer. I went back and rechecked the hose between the mass air sensor and the throttle bodies and found a poor seal. Redid the clamp and sealed the hose better. Turned the key and she fired right up. Now I think there will never be another faired bike in my future as I hate putting all that plastic back in place.

Mike Hankinson Hudsonville MI

MichiganMike said:

The K75 runs again... Now I think there will never be another faired bike in my future as I hate putting all that plastic back in place.

Mike Hankinson Hudsonville MI

Click to expand...

Riding a naked K75 (windshield only) makes life abit easier when it come to part removal and checking.

Good on yah for finding and fixing the problem