1992 K75s fuel delivery problems

I just bought a 1992 K75 which sat with only a small tarp cover for over 2 years. It wasn't running but I installed a new battery as a start toward at least getting it running. When I first tried cranking it there was some weak firing but didn't respond too well to the throttle as if running way too lean. I cranked it again using the "choke" full on resulting in gasoline accumulating in the exhaust pipe after about 10 to 15 seconds of cranking. It did not fire even once. I decided to try leaning it down by clamping off the fuel delivery line between the pump and fuel rail (i know this would not be advisable) and it ran great for about 5 seconds until the fuel line was empty. I tried again to crank it normally and.....nothing. To see if the fuel delivery line was pressurizing, after.about 10 minutes I loosened the fuel line at the fuel rail and it still had considerable pressure. I let it sit for a day and now it starts and runs terribly like the mixture is too lean but the plugs are sooty but dry and it won't really run at all at small throttle openings. This is my ninth BMW over 20+ years, five of which were fuel injected but I have never encountered anything like this. Any ideas would be appreciated.

You may have popped the fuel filter off the hose inside the tank, or even ruptured the filter by clamping the hose between tank and rail.

Thanks, Lostboy. I'll check that out; I have to remove the tank anyway to attempt to bleed the front ABS unit.

[QUOTE=broadstone;826055]Thanks, Lostboy. I'll check that out; I have to remove the tank anyway to attempt to bleed the front ABS unit.[/QUOTE]

You don't have to remove the tank to check the filter or bleed the ABS.

That would really be great as I wasn't looking forward to removing the entire fairing to achieve that as I read on several web sites. I can't see the ABS unit so do I assume its necessary to remove the fairing to get at the ABS or at least the radiator screen? Thanks for your input. Jim

the ABS modulators are the bean can looking things at each passenger footpeg. the right 1 is for the rear brake and the left 1 for the front brake. Each. has a bleeder valve.

And the fairing does not need to come off to remove the tank (but you do need to learn how to remove the tank). All the relays are under the tank. The radiator cap is under the tank. You need to periodically (like yearly) check the coolant level AT THE CAP not at the overflow bottle.


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How about opening the three brass throttle body screws to feed it more air?

You'll need to balance the throttle bodies at some point, but in the interim you could remove the three brass screws, clean them with carb cleaner, screw them in all the way GENTLY, and then back them out 1.5 to 2 full turns and see how she runs.

[QUOTE=TimTyler;826141]How about opening the three brass throttle body screws to feed it more air?

You'll need to balance the throttle bodies at some point, but in the interim you could remove the three brass screws, clean them with carb cleaner, screw them in all the way GENTLY, and then back them out 1.5 to 2 full turns and see how she runs.[/QUOTE]

That only primarily affects the idle balance between cylinders, not mixture.


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This won't be an easy one. There are too many things to do. I think some preliminary work needs to be done even before reasonable troubleshooting can begin.

Two years under a tarp leaves both the electrical and the fuel system suspect. The fuel in the exhaust could be caused by sticky fuel injectors or could be caused by fuel injectors pumping fuel into cylinders where the spark plugs are failing to fire.

You should get an in-line spark plug tester or good inductive timing light - either of which can be used to observe the spark pattern while cranking. Neither will flash if a spark plug is badly fuel fouled, but otherwise will show if there is spark or not.

I would start with that. But I would also remove the fuel tank and clean the electrical connections at the coils, the ignition module, and the engine computer. While I was at it I would clean any other connections that looked the slightest bit suspect. This will save trouble later I suspect.

On the fuel side I would empty and clean the fuel tank. I would make sure the fuel pump and filter are clean. (new filter) I would try to pump known good new fuel dosed with Chevron brand fuel injection cleaner with Techron into as much of the system as I could and hope the injectors are not sticky.

After that preparatory work I think you can do reasonable trouble shooting if you still need to.

Thank all of you very much. I feel a bit embarrassed that I listened to someone on another site about the location of the front ABS modulator. The bike is still on a trailer with the left side next to a wall so it's location wasn't apparent. Anyway, I bled the modulator and the front calipers again but I still don't have any significant lever pressure so I suspect a not too healthy master cylinder. I still believe that, somewhere along the line, I'll also discover frozen caliper pistons but that's something I can deal with. Is a significantly rusted ABS counter ring likely to be a problem? Because it is an inductive signal from the counter, rust shouldn't be a problem, should it? Again I thank you all for your helpful input.

It is VERY common on an early K that has sat for a while, for the rubber fuel pump vibration damper to start to dissolve. The dissolved rubber gets sucked up by the pump and plugs the filter and injectors.

BEFORE you try to start it again, remove the pump and inspect the area in the tank under the pump pickup. It should be clean and shinny.

Inspect the vibration damper. It should have the consistency of a tire. If it s soft or gooey, it needs to be replaced.

After you are sure the tank and filter are clean, you need to do a fuel pressure test. A bad pressure regulator or plugged filter or injectors can cause the problems you have.



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I've made a little progress in that I now have a little pressure at the brake lever even though I got zero air bubbles at the front ABS modulator or any movement of the fluid remaining in the bleeder hose. The master cylinder is leaking so that's part of the problem at least. I've decided to take the fuel issue to the experts but will battle the brakes on my own (well, with guidance from you guys). BTW, what is the purpose of the diaphragms in the fluid reservoirs. I removed them while bleeding to increase the fluid volume. I assume they are there to reduce sloshing of fluid in the reservoir. Progress!

The diaphragm is to keep air (and hence moisture out of the brake fluid).

If your master is leaking STOP. That is the source of your brake problems. It either needs to be rebuilt or replaced. You will only end up trashing your paint from dripping brake fluid if you continue.


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Thanks 98lee. I've ordered the master cyl rebuild kit and will use the time for delivery to locate and buy a circlip tool for removal of the piston. I've protected the paint with a plastic bag on the fairing covered with a towel.