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'87 K75s Fuel Pump Filter Gauge Breather Hose Routing - Fuel Pump

kentuvman

kentuvman

New member
Before I consider my job done of replacing new hoses, fuel pump damper, and filter inside fuel tank I do have a question I'm not sure about:

I know for sure I removed a rotting fuel line off the bottom of that pump (see picture).
What I'm not sure about is where it connects to. I believe it connects to the vent pipe at the top of the tank - the rotting hose was @ 12" long.

Is this correct?

Thanks much.
 

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This picture shows the vent pipe at top of tank, with smaller black vent hose connected (right below the larger diameter fuse hose). in this picture, fuel pump is not yet re-installed in tank but I do have the solid black vent hose connected to the vent pipe at top of tank
 

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That is the correct routing for the vent hose. Your other post about the main hoses sounds like you put a fuel hose on the crankcase vent at the rear of the fuel rail?
 
Thanks, Ron

I must've used the incorrect words - I used new fuel hose going that attach to fuel rail and used existing pipe hose that is in good shape - I never changed it. From what I can see, it goes into the engine below the airbox.

Haynes refers to it as forward hose on left side as a "return hose"
 
Last edited:
The front left hose is the return. It goes between the air box and the fuel rail where it connects to the FPR. From there, it goes to the fuel rail rear connection.

When I replaced my hoses at the 18 year point, they were rock hard and would turn on the FPR( not leaking) If it looks like the return is old, you might consider removing the airbox and changing the fuel hose and the vacuum hose from the FPR to the fuel rail.
 
Thanks again, Ron

Is the FPR (fuel pressure regulator) supposed to be fuel rated or is it considered a breather type hose? Does fuel constantly travel through it?
 
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All 5 hoses that carry pressurized fuel should be rated for at least 100 psi. The two that are inside the tank should additionally be submersible rated.



:dance:dance:dance
 
Had enough leftover fuel hose to replace FPR line - feel much better getting it replaced - there were cracks on both ends of hose where it attached to tank & FPR.

Thanks again.
 
Did you also replace the one that runs from the rear of the fuel rail to the fuel pressure regulator?




:dance:dance:dance
 
Yes I did.

Meanwhile, I put everything back together and went to start the bike.

It hesitated and hesitated and will run at a very low rpm but the second I touch the throttle it dies. It won't run with the choke.

I'm suspecting I may have put the fuel filter backwards.

If you look at the picture above, it looks like I've got the wrong end facing the short hose.

Going to double check and will report back.

UPDATE:

Looks like fuel filter was in wrong way.
Motor starts but can't get off idle.
Pulled fuel hose off rail and pump is pumping fuel into injectors.
We did rebuild the fuel/water pump - that seems to be turning okay.

Must be a fuel delivery issue but what?
 
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kentuvman said:
Yes I did.

Meanwhile, I put everything back together and went to start the bike.

It hesitated and hesitated and will run at a very low rpm but the second I touch the throttle it dies. It won't run with the choke.

I'm suspecting I may have put the fuel filter backwards.

If you look at the picture above, it looks like I've got the wrong end facing the short hose.

Going to double check and will report back.

UPDATE:

Looks like fuel filter was in wrong way.
Motor starts but can't get off idle.
Pulled fuel hose off rail and pump is pumping fuel into injectors.
We did rebuild the fuel/water pump - that seems to be turning okay.

Must be a fuel delivery issue but what?
Click to expand...

Check the airflow meter in the top of the airbox. You may have disturbed it when you removed the box during the fuel line change.
 
We're Purrrrring Now!

Thanks guys for your help!

After going back to the air box, I discovered I did not have the rear portion of the hose secured to the plenum. Went back in and took care of it. Thought I'd have to remove the radiator but after more than several attempts I was able to secure it using a long screwdriver, approaching the hose clamp from the top rail of the frame - took some focus but she's running now!

Also learned how to figure out which vent tank is which, on the rear of the K75 by blowing on the pipe with a hose and feeling where the air comes out around the filler cap.

Very grateful to this group of professionals who instill confidence in a shade tree mechanic like me.

So, now that it's running . . . how come you can run a carbureted engine w/out the air filter but not on a fuel injection engine?
 
kentuvman said:
Thanks guys for your help!

After going back to the air box, I discovered I did not have the rear portion of the hose secured to the plenum. Went back in and took care of it. Thought I'd have to remove the radiator but after more than several attempts I was able to secure it using a long screwdriver, approaching the hose clamp from the top rail of the frame - took some focus but she's running now!

Also learned how to figure out which vent tank is which, on the rear of the K75 by blowing on the pipe with a hose and feeling where the air comes out around the filler cap.

Very grateful to this group of professionals who instill confidence in a shade tree mechanic like me.

So, now that it's running . . . how come you can run a carbureted engine w/out the air filter but not on a fuel injection engine?
Click to expand...

The airflow meter in the top of the airbox "tells" the computer under the seat how much air is going into the engine. Your leak was downstream of the meter, so it was unmetered.
 
I watched your thread about fuel lines routing .

Earlier today I asked which way the intank fuel filter was suposed to go. I got several answers and the bike is running again.
That's what caught my eye ,and I followed all your thread.

You mentioned having the Haynes service manual. I got that with my bike , and Clymer's much thicker one too.
You can get a free download of the OEM BMW service manual for your 1987 K 75 RT if you google " carlslater service manuals " or just "carlslater.com"
I got my 1991 K75 RT about 7 weeks ago , and found when in doubt look it up in all three . one should make sense, or at least explain things the others didn't do so good ...
Glad your bikes purrring again.
 
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