My 94 R1100RS started making a louder higher pitched whine noise at about 95,000 miles. I suspected I'd have to replace the pump but after talking to several BMW techs and finding out the pump almost never fails I decided to take it out of the tank and look at it. I also have an R1150GS so I could easily hear the noise difference. When I removed the filter and pump from tank I noticed the filter had water in it. I suspect the filter was close to clogging causing the pump to cavitate thus making the noise. Sometimes the filter seam can fail inside the tank causing a loss of fuel pressure and the bike quits. I suspect this also happens when it starts to clog. Anyway new filter and cleaned several liters of water out of bottom of tank and noise was back to normal. The filter isn't a easy roadside repair unless you move it to outside the tank. I did it on the GS for ease of maintenace. Some GS sites have details on what you need to do it. The pump is expensive and really rarely fails. BMW doesn't sanction putting filter outside tank. Thier reasoning is if filter fails inside tank you don't have an external fuel leak probably on your leg. Safety first, but I fiqure if it's outside the tank it's easier to maintain and if you hear the hi pitched whine you can drain whatever is clogging it quick before it clogs and maybe fails.
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