1991 bmw k75s

[Alex Naccarato]

Hey guys, so I bought this bike a week ago and have done some work to it but I’m still have a few issues. 
-I replaced the fuel pump, new battery, cleaned the tank out, put oil in the cylinder heads, changed spark plugs, checked my MAF sensor. 
my issue is that it will start and turn over  with the choke open all the way and the throttle maxed out, it idles at 3000 and I can turn the choke down one notch and it idles at 1000, when I try to rev it, it dies, when I turn the choke completely off the bike cuts off. 

[roadscholar]

This is about as unprofessional opinion as you can get but I bought an E36 M3 that acted similar. Discovered it had an air leak at the intake plenum, once that was sealed it ran fine.

 

Also had a K75RT years ago that had sat a long time, replaced the fuel pump, sending unit, and fresh gas, all was well, great bike.

[dirtrider]

10 hours ago, Alex Naccarato said:

Hey guys, so I bought this bike a week ago and have done some work to it but I’m still have a few issues. 
-I replaced the fuel pump, new battery, cleaned the tank out, put oil in the cylinder heads, changed spark plugs, checked my MAF sensor. 
my issue is that it will start and turn over  with the choke open all the way and the throttle maxed out, it idles at 3000 and I can turn the choke down one notch and it idles at 1000, when I try to rev it, it dies, when I turn the choke completely off the bike cuts off. 

Morning Alex

 

If you have good fuel injector spray (injectors & injector inlets are not plugged) then make sure the air flow sensor vane is moving smoothly & properly.  And as  Roadscholar mentioned,  check the intake between the engine & air flow sensor for no signs of air leaks. It doesn't take much of an air leak to make the engine run poorly. 

[John Ranalletta]

10 hours ago, Alex Naccarato said:

Hey guys, so I bought this bike a week ago and have done some work to it but I’m still have a few issues. 
-I replaced the fuel pump, new battery, cleaned the tank out, put oil in the cylinder heads, changed spark plugs, checked my MAF sensor. 
my issue is that it will start and turn over  with the choke open all the way and the throttle maxed out, it idles at 3000 and I can turn the choke down one notch and it idles at 1000, when I try to rev it, it dies, when I turn the choke completely off the bike cuts off. 

A friend gave me his k75 that had rotted in his garage for years.  I replaced all the gas tank innards, had fuel tank holes welded, etc.  Took it to two "experts" who couldn't determine why it would start but not run smoothly.  The problem was a faulty fuel pressure regulator according to the young man to whom I'd sold the K out of frustration.

 

This is from a K forum. Hope it speaks to your problem.  Good luck.  BTW, attempts to work on the K resulted in a garage fire, fire dept crew visit and a visit from county mounties with hands on sidearms. Interesting night.  I'll never forgot that bike.

 

The fuel comes out of the pump (capable of 100psi) in the tank, through the filter (also in the tank),and out the rear nipple on the left front lower edge of the tank. It goes through a hose (about 8" long) to the front of the fuel rail, where the injectors draw the fuel from.  At the rear end of the fuel rail is a hose that goes to the fuel pressure regulator. The fuel pressure regulator is hidden behind the throttle bodies between the throttle bodies and the air filter box.

The fuel pressure regulator bleeds off any pressure above 38psi. That bled off pressure goes forward through a hose back to the tank through the nipple just forward of where it came out of the tank.  So the fuel rail pressure should stay at about 38psi unless the fuel pressure regulator is defective. It can fail either too high or too low.

Don't EVER rely on previous owners troubleshooting when trying to get a bike running. VERIFY!!! Remember, he couldn't get it running before he sold it (thereby losing at least $1000 in the sale), so he wasn't a very good troubleshooter.

The best way to test the pressure is to TEE a gauge between the rear of the fuel rail and the hose that goes to the regulator.  You have already pulled and inspected the pump,damper,pickup sock and inspected the bottom of the tank where the fuel is picked up and CHANGED the filter, right?

IF those are OK, the other fuel issues might be clogged injectors, failed regulator (TEST pressure!), or a sticking air flow meter.

 

 

[szurszewski]

1 hour ago, John Ranalletta said:

BTW, attempts to work on the K resulted in a garage fire,

 

@Alex Naccarato  As it happens, I also have a "project" K75s that came to me after the previous owner set his shop on fire trying to sort out a fuel system/pressure issue. I haven't actually gotten into that bike yet, thus the quotes around project above, so I have no useful advice, other than, don't set your garage on fire!

 

 

[John Ranalletta]

Does Alex live in wisconsin?