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Hello All

I own a 1997 R1100RT and I am having a problem with fuel spitting back into the airbox, The BMW Mechanic suggested the air pressure was not correct and I cannot seem to find any infomation on the Air Pressure Regulator and no posts on this site seem to cover it

The bike has had the injectors tested, the cpu tested, O2 sensor checked, every thing that has to do with the fuel system (I was told) is in specs

Has anyone had this problem, and how was it fixed. I'm up to $500 AUD in parts alone so far trying to fix this problem ($500 includes a 120k service, but to labor charge yet)

Any help would be a great help

Ron and Wendy
Ulysses Top End Branch
Darwin Australia

Do a cylinder compression check. If it's low, you may have intake valve or piston ring sealing problems. The "spitback" you're seeing . . . . I'm guessing it's oily fuel . . . as would happen with excessive blow-by.

Forgot to mention the symptoms.

When I bought the bike, I picked it up and rode it 6000Ks in 5 days to get back home to Darwin. Everything was fine and it was a joy to ride my first BMW and another first it is a shaft drive, my first one

After arriving in Darwin I rode it for approx 2 weeks and had fitted new tyres and then waited for paperwork to arrive so I could register it in the Northern Territory (Australia). During the 4 week period that I was waiting, I started the bike every Saturday and ran it till the temp gauge was 1/2 way then shut it down

When the paperwork arrived I took the bike to the Registry Office and on the trip there, every time I had to stop and the bike went to idle, it would run roughly and nearly stall. After returning home I booked the bike in for a service hoping the tune up would fix the rough idle but that’s as far as it got and that’s as far as the mechanic has got

My wife completed her Advanced Riding Course on the weekend (she passed and wants to steal my BMW) and the mechanic from where I have the bike in for the service and the problem, also was on the course and he informed my wife that the “bloody thing still won’t run properly” He is chasing the Air Regulator Pressure settings through his contacts and I informed him that I’ll try the forums and search the net for any info

I'll see if I can get the figures from the compression test the mechanic done

So, this is where I’m at… waiting for info and/or my bike back
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There are a lot of roads out there, I want to ride them.
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Only a motorcyclist understands why a dog hangs its head out the window

How can fuel spit back into the airbox? And is there such thing as an Air Pressure Regulator?? Is it instead the fuel pressure regulator?
Could it be that you are finding oil in your airbox that came from the crankcase breather? If so, are you sure you did not overfill with motoroil?

Two things, first, do as Cyclerob suggests and verify that the valves are properly seated.

Secondly, when I read this,

During the 4 week period that I was waiting, I started the bike every Saturday and ran it till the temp gauge was 1/2 way then shut it down

That is a definite NO NO. on an air cooled BMW, as soon as the engine is started, you ride off period, no ifs ands or buts. I suspect that you have overheated something and as Rob suggested, your valves are not seating.

G'day Ron,
You have two problems that may or may not be related. One is the rough running and the other is the fuel in the airbox.
Firstly, you'll need to determine whether the airbox contains fuel or oil. I would expect that fuel would vapourise in the airbox and be consumed through the intake rather than just sit there. It's possibly a mixture of oil and fuel.
If it is in fact fuel, I would suspect an intake valve is leaking causing some fuel to spit back through the intake.
For some possible causes, have you tried looking through the FAQ at http://www.bmwst.com or http://www.ibmwr.org ?