Pillion exhaust fumes on GS1100G...

[tkent02]

Took my wife out on the 1100G for the first time since I got it. About an hour, some highway speeds, couple canyons, some mountain twisties, back across town, the same stuff we do quite often on all the bikes. This on a completely stock bike, airbox, exhaust, all of it, and no fairing or bags on the bike now. The exhaust pipes are in good shape with no leaks, the carburetors are tuned well, the bike runs very nicely indeed.
She informed me she was breathing exhaust fumes, very badly. It was worse under power, worse at higher speeds, but some fumes all the time. She has ridden on a lot of bikes with me, she knows what she's talking about. As a test I put the choke on while cruising down a hill slowly, right away she said "Whatever you did it just got a lot worse"
This was not the little wisp of exhaust you get once in a while from the wind blowing in a weird way from behind, it was serious bad air, all the time. I ended up leaning way down on the tank as much as I could to give her fresh airflow over the top of me, she said it was fine like that. I have never noticed any fumes riding this bike solo.
So, anyone have any ideas about what might be the cause of this problem? Anyone else notice this on an 1100G or any other big GS?
I know aerodynamics is weird science, but I can't understand how exhaust can come from the tail pipes up to the inside of her helmet, when it doesn't happen at all on any of the other bikes.

 

[Nessism]

That suck Tom. Not sure what to suggest other than maybe leaning down the pilot screws and checking the jetting to make sure it's stock. You are at elevation also so maybe you should try some leaner jets and see if it runs cleaner.

Hope you figure it out and good luck.

 

[tkent02]

I can check, but it runs very well, the plugs look right. It has CV carbs, they compensate for elevation quite well, it runs fine up at 14,000 ft, down here at 5,500', and anywhere in between. But think this through, fumes shouldn't be getting there no matter how rich it is. My 650G is quite rich, I've ridden behind it on other bikes, you can smell it easily, but no complaints from the peanut gallery on the back of that one. A lot of bikes are rich and poorly tuned, I have never heard of a passenger breathing fumes.

 

[Griffin]

Bad petcock leaking excess gas into the airbox? Breather hose attached to the airbox?

I'm guessing if she's smelling it and you're not, then it must be coming from an area behind you, but not behind her. The airbox seems to me the likely source of the fumes.

 

[tkent02]

Good idea, I will look into this....

 

[BigD_83]

Tom,

How did this end up?

Jess mentioned the same thing during a ride on the 650, and like your 1100G, everything seems to be jetted well and in good repair.

 

[chuck hahn]

She smelling raw gas or exhaust gases? I was thinking maybe just like when you leave the hatch open on a Mini Van or something and you smell the fumes that get sucked in to the low pressure area created behind the vehicle?? Maybe this particular bikes seating positions are making fumes basically wrap thier way up and around her???

 

[Steve]

Chuck, keep in mind that this must have already been resolved. :-k

The original post date was almost two years ago, and he has not complained about it since then.

Not sure if he fixed the bike or simply doesn't take his wife for any more rides, though.

.

 

[chuck hahn]

I got that..but like Big D i was wondering what the solve was. I havent heard this complaint before and found it as a very obscure event. I was asking the questions to see if anything i thought could be the culprit had anything to do with it.

I have read in van and other vehicles manuals (with a back hatch or door) that if you leave them open the eddy behind the vehicle actually sucks exhaust fumes in to the passenger compartment...was wondering if this may have been the case here.

Behind the legs would probably be a good eddy area for a passenger???

 

[Steve]

I have been riding bikes of various sizes with windshields and fairings since 1976 and have not experienced this, either.

Just wanted to make sure that you knew this was not a new occurrance, but a resurrection of an old thread.

.

 

[chuck hahn]

Oh yeah I saw the original post date, but this was the first I recall the thread. Seems a curious thing ..doesnt it. You know what i mean by that low pressure area thing right?

 

[Steve]

You know what i mean by that low pressure area thing right?

Oh, yeah. Depending on the aerodynamics of the fairing, it is not uncommon to be pushed forward while riding "at speed", due to the air that was pushed out of the way closing in behind you.

The effect on the rider (driver?) is lessened when a passenger is aboard, but that only moves the effect farther to the rear, and the passenger feels it, instead.

.

 

[TheCafeKid]

....which is exactly why I don't like a windscreen of any substantial size on my bikes. The feeling of something pushing on the back of your head all day gets annoying. That, and in the summer it's awful hot behind one of those on a GS. That dead air area right above the tank draws all of that hot air from around the motor up...

 

[BigD_83]

Chuck,

I hear what you are saying about the eddying, but I have a hard time imagining it being a factor at any kind of speed.

For us, the exhaust is mainly a low-speed/low air flow situation like city riding, and I thought it was related to a weak burn due to a dying coil, but that problem has been fixed, and Jess is still mentioning the smell.

It's an unusual one, and I didn't even think about it until I saw this old thread title looking for something else 1100G related. Got me curious as to whether it was ever resolved.

 

[BigD_83]

....which is exactly why I don't like a windscreen of any substantial size on my bikes. The feeling of something pushing on the back of your head all day gets annoying. That, and in the summer it's awful hot behind one of those on a GS. That dead air area right above the tank draws all of that hot air from around the motor up...

TCK,

that's a good point. I've never ridden a bike with a large fairing, but I could see how that would work.

 

[chuck hahn]

I know its really weird..Kinda a head scratcher for sure.

 

[bwringer]

The solution, obviously, is to alter the pilot's aerodynamic profile.

See your local burger joint or taqueria for details.