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Discussion Starter · #1 ·
So, I have the 99 Canyon Red version K1200LT. I can remember as far back as Hot Springs and other venues where the warm weather almost killed the ride. In Calgary, the issue was not as troublesome but when I brought the bike into warm weather I got backfiring, hesitation and all kinds of troubles. Those problems really got worse in the last two years. I did not go through all the motronic, wire cutting, temperature sensing fixes discussed. I lived with it until recently when it was suggested I just get another bike. That was the challenge.

Earlier this year (2012), I could not start it after leaving it alone for a few months. It was offered by my knowledgeable brethren that the fuel filter was probably plugged . I went inside the fuel tank for the first time since 1999.

Upon inspection there really wasn't much junk in the tank which was good to see. The fuel filter was clean and flowed without restriction. The fuel pump when tested on the bench erupted with fuel so I figured it worked. The little filter sock on the bottom of the fuel pump was broken and messy so I replaced with a $6 larger sump filter from Autozone (see photo) and it just presses on easily to the sump side of the fuel pump.

I still had not found any problem so I decided to change the fuel filter anyway and disassembled the fuel lines and components that were hidden inside the tank. While checking the lines I noticed a small crack in a 180-degree piece of original hose that sits inside the tank. It is after the fuel pump and is a production BMW piece so it no doubt affects other bikes. I blew into it and it leaked like a sieve. BINGO!

The bike was reassembled and I can now say that it behaves like it did new in 1999. All the hesitation, roughness, backfiring and other nonsense is gone. It accelerates properly and behaves like it hasn't in many years. I offer this little tidbit because if my bike has this problem I know others will have the same issue. It isn't easy to find and many people might not even look for it given all the knowledge about motronic versions, temp sensors and other culprits. It doesn't leak fuel externally, this leak just pumps fuel back into the tank. The split in the line probably started small and grew over time until the bike just wouldn't start and run.

So before you go cutting wires, replacing moronics or buying a new bike because your older LT backfires, hesitates, has rough starting, poor acceleration and really sucks in hot weather--perhaps look at this little piece inside the fuel tank. For a few bucks you might find yourself with a new bike. If you're going to do a similar inspection on your LT, spend $20 and get the sump filter ($6), fuel filter ($4) and a few feet of R9($5) fuel injection line and some connectors($5). That should do it if you have a similar problem.

best,

Paul
Daytona Beach and Calgary
 

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I hope you got immersion rated fuel line. I recently learned that the stuff inside the tank is different than regular FI line. Good post. All the symptoms make sense as the crack would cause low fuel rail pressure and thus lean conditions in the combustion cylinders.
 

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Wrencher Extraordinaire
2005 K1200LT
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15,061 Posts
You got luck on the hose as usually they no longer will even start when that baby lets loose. Thanks for the tip on the fuel sock. Have a PN to share? Or was it just on the rack at Autozone?
 

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Discussion Starter · #5 ·
Autozone carries a whole range of fuel strainers in the $10 range with the snap-on connection that is common to many fuel pump inlets, including the LT. There is FS22, FS10, FS3 and many others. I think the photo I submitted is FS3. It is much larger than the stock BMW one which prices around $40. Here's a photo of the 99 inlet strainer (original) torn and useless.

Like I said in the previous post, you would not normally see the leak in the offending hose. It was not visible until I took it apart and started bending it. If someone has similar problems and doesn't want to go into the tank I think the best way to check would be to put a fuel pressure gauge on the outlet line from the fuel tank. Let it pump up and watch what happens. That can prevent taking the tank apart if pressure holds and the fuel pump stops running. If pressure drops or the pump won't stop then I guess there's a problem in the tank somewhere.

I can almost bet that 180 tight turn part from BMW is a plague on these bikes. If the design has changed, that would probably suggest it really was a problem. What's the design on newer LT's after the fuel pump?
 

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Discussion Starter · #6 ·
I concur on the need to use the right fuel injection line. I believe I replaced the piece either with the line that comes with the new fuel filter or the R9 line I bought from Autozone. This note from Gates rubber identifies that R10 spec is for submersion. I may end up going back to the tank for a fix some day if the R9 fails inside the LT tank.

http://www.gates.com/oreilly/tech_tips/PermeationResistantFuelLineHose.pdf

So, R7 is out completely. R9 is for external high pressure fuel lines and R10 is for submersion in fuel systems.
 
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