Leaning left causes engine to run rough. Still curious. - BMW Luxury Touring Community
 
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post #1 of 10 Old Jan 12th, 2010, 10:32 pm Thread Starter
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Leaning left causes engine to run rough. Still curious.

For about 3 years now and some 25k miles I have been trying to determine why my '99 LT runs rough when the bike is leaned even slightly left. It's most noticeable at idle, dropping about 100 rpm's, and it can also be felt at road speed. It runs perfect when it's straight orleaned right. It's not affected by the fuel level. It has 71k miles and has been well maintained. No other issues. I've asked 3 dealers and have been told they have not seen this problem on another bike and it's not so bad that I want to spend a grand on diagnostic service. I've test run other LT's and they did not have this problem. I'm wondering if anyone else has noticed this problem on their LT and if there are any takers on what might be causing this. It's not a major thing, more of a curiosity. Could something be going on with the oil or oil pump? The level is where it should be - never over or under.
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post #2 of 10 Old Jan 13th, 2010, 8:22 am
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Re: Leaning left causes engine to run rough. Still curious.

Just a wild guess or two.

Since at idle is there a chance that throttle linkage is moving slightly due to turning the handle bars when leaning?

Could the mass air flow sensor be moving slightly when leaned. (Note: not sure if this is a butterfly type or not?)

Now let the experts chime in.

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post #3 of 10 Old Jan 13th, 2010, 11:28 am
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Re: Leaning left causes engine to run rough. Still curious.

Quote:
Originally Posted by bigbear
Just a wild guess or two.

Since at idle is there a chance that throttle linkage is moving slightly due to turning the handle bars when leaning?

Could the mass air flow sensor be moving slightly when leaned. (Note: not sure if this is a butterfly type or not?)
Good thoughts, but no mass air sensor on the LT ( in fact, no airflow sensor of any type).

I also don't have a good idea as to what's causing this. I believe my first step would be to pull the left side tupperware and start hunting around for an electrical issue which could be caused by a wire shifting when the bike is leaned to the left -- for example, if one of the wires from the throttle position sensor has an insulation failure spot and the left lean causes it to contact metal and ground out -- that could cause the Motronic to alter the fuel delivery. Same could be said about the O2 sensor. Coil wires are another possibility in the same general area.

Another non-electrcal possibility would be a vacuum leak, where a cracked hose "opens up" for some reason when the bike leans left -- I'd check both the four hoses leading from the charcoal canister purge solenoid to the individual throttle body inlet nipples, and the crackcase breather hose, which is notorious for degrading/cracking with time (a pita to check -- buried under the frame backbone, above the engine block).


Sorry I can't be of more help than this -- good luck with the hunting!

Mark Neblett
Fairfax, VA

Last edited by mneblett; Jan 13th, 2010 at 2:35 pm. Reason: typo
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post #4 of 10 Old Jan 13th, 2010, 2:29 pm
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Re: Leaning left causes engine to run rough. Still curious.

You might want a helper..

Remove tupperware,
Start bike, lean to left
Spray "wd40" around the base of the "intakes"

If engine speed varies, it is prob. a leak in an intake fitting.
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post #5 of 10 Old Jan 13th, 2010, 3:21 pm
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Re: Leaning left causes engine to run rough. Still curious.

If you are having problems when you lean left (CNN) then you have to be careful. The left will suck the wind right out of ride and destabilize your every effort to maintain balance.

Try leaning right (FOX) and see if you can't be fair and balanced. I know that is is hard to turn right when you are leaning left, but go slowly and it can be done.

Ken it is a joke, don't get serious.

Ride 'em if you got 'em.
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post #6 of 10 Old Jan 13th, 2010, 5:15 pm Thread Starter
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Re: Leaning left causes engine to run rough. Still curious.

Some good suggestions, thanks. Looked it all over again today and didn't find any suspect hoses or leaks. All still look new and are on tight and routing looks good. I might add it does this when it's leaned left regardless of where the bars are. Even leaned a tiny bit. Seems gear noise is a little more pronounced when it's doing this, maybe because of the engine lagging a bit. Weird problem. Any thoughts on slight fuel starvation? Don't know exactly how it all works on the LT. It doesn't do this any more or less when the tank is empty. I use fuel stabilizer in it year round and always run high octane. Also makes no difference if I'm in the saddle or not. If I try to start it with the bike on the side stand, it will idle very slow. Maybe something to do with oil draining into the head? Always use the BMW oil.
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post #7 of 10 Old Jan 14th, 2010, 2:59 pm
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Re: Leaning left causes engine to run rough. Still curious.

Try giving each of the injector connectors a tug. No need to remove tank just a bit of tupperware. Mine ran like crap around 3,000 rpm but was ok below and above that after my clutch job. I traced it to an injector connector that was not fully latched. I snapped it in and all was well.

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post #8 of 10 Old Jan 15th, 2010, 3:46 am
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Re: Leaning left causes engine to run rough. Still curious.

Check the fuel hoses IN the tank. If you replace them be sure to use SAE 30R10 hose as this is the ONLY hose that will stand up to being immersed in gas inside and out.

Last edited by Morley; Jan 15th, 2010 at 3:56 am.
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post #9 of 10 Old Jan 15th, 2010, 8:02 am
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Re: Leaning left causes engine to run rough. Still curious.

I just went through a mysterious fuel problem on my LT. Have you performed an canisterectomy? This procedure is widely recommended for most phantom rideability issues, It didn't help me, but, it was the first and easiest step.

The fuel rail is located on the left side, if there is some foreign substance, water perhaps, accumulating in fuel rail it could affect your idle issue.

My local motorcycle Rabbi highly recommends Chevron/Techron fuel injection cleaner,
a partially clogged injector could cause a minor disruption of the spray pattern when leaned.

Go simple first. Around the fuel rail it's a wire/cable/hose jungle. There may be binding of some hose/wire bundle with the throttle linkage that runs below the fuel rail.

On a lighter side, I guess this will eliminate you from the NASCAR Sprint oval races.
There's still the road courses!

Good luck.
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post #10 of 10 Old Jan 15th, 2010, 3:08 pm
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Re: Leaning left causes engine to run rough. Still curious.

Ok, I am still waiting for some comedian to bring up the connection between left leaning motorcycles and left leaning governments running rough.
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