Wondering if anyone else had this happen. When I come to stop after riding for a while I smell gas. When I speed up the smell goes away. I have stopped and checked but cannot find any fuel leaks. It apparently is only gas vapors. The bike, an '85 K100RT, runs perfect and I didn't know if this is normal.

nick.... there are many new additives in the fuel that permeate the fuel lines these days ....
sadly the rubber in our old beasts ages and gets worse

but there are also different (but harder to get) rubber lines available

look for sae 30r10 type fuel lines as these have a lower leakage by quite some difference .

good luck

Hey Nick,

I will echo what Charlie said about replacing the rubber as it is never in great shape after 25+ years. Didn't know about the uprated hose, and that might be a great option if you're so inclined.

OG

SAE30R10 rated hose is suitable for full immersion in fuel.

Don't use it on brake lines.
RT

I have the same issue but cannot find any leaks. I will look at the fuel lines.

one thing i did think of whilst doodling away was ....

is the breather under the tank giving off the smell ...i would imagine that when the bike changes from higher revs (slightly less flow returns from injector rail ) and the preasure may change as one comes to idle .....does this mean there is a slight release of fuel droplets out into the under tank bucket ???

just a thought

They all tell you its the rubber fuel lines but not which one!
There is a breather in the tank which runs from the nylon filter basket on the bottom of the pump up to a breather just inside the tank beside the filler cap.
It turns to liquorice after a lot of years due to fuel additives and breaks up.
I have never replaced mine and, as you say, you get the whiff of petrol occasionally when you stop. Think the fairing makes it more noticeable or if its warm. Not a problem very often here! June and its 11C at noon.
If you do replace it, use the proper grade as it is immersed in petrol continuously.

well to expand on what john said .....
i would be thinking the highest loss places would be
, the high presure line from the tank to the fuel rail ,, the small piece around the back to the presure regulator .....after that the lines have slightly less presure as there is little restriction back to the tank, but because it is a high heat area still needs attention.

i would expect those lines to have the most loss (permeability )
rates of 550g /sq mtr/day have been quoted and are common especially with older hose ....of which much is not rated for unleaded fuel to start with ...thus the wiff of fuel we get when standing still idling .

the lowest rated fuel line i have seen for unleaded high presure use is sae 30r9 with something like 5-10g/sq mtr/day losses


john that line (1/4 inch ) leaves the filter cage and joins to a metal line at the top of the tank ,turns slightly then goes to the bottom of the tank out the breather ......the breather hole at the side of the filler cap is metal all the way through the tank to the under side

Hi there, know this is an older post, but I seem to be having the same problem.

I've replaced the seals in the fuel cap (well the Rubber main seal on the tank, and the foamy type that you can get to, behind the 3 screws on the cap. Wasnt game to try and pry off the centre piece with the 3 tangs to get to the steel washer and parts)

Seems to be only happening when its warm, this morning on the way to work I almost felt like I was "chroming" the fumes were that bad..........
But then I stopped to fill up, and the fumes were much reduced, almost gone.

So with a full tank having a less fumy result, is this a sign of what I should be looking at to try and fix it???????

Andy, check the underside ofthe tank and fuel lines. Look at my thread here I had very similar symptoms.
88KE

Yes 88KE, a leaky tank at the lowest point - under the fuel pump - would be the first place to look for me.
Paul.

Thanks 88 & Paul, I'll check it out..........Could it be a sign of the hoses inside the tank nearing the end of their life, or hoses to the fuel rail?
I have fixed one hole on the bottom of the tank at Xmas time with the Permatex stuff just near the seem, but thats holding up fine.
My girl has is just about to click over 170,000Klm, and to celebrate, she's getting a new cam chain and tensioner, plugs, oils, aircleaner and the list goes on.........actually the list doesnt really seem to end.........but of all the bikes i've owned over the years, there isnt another that i would have dreamed of still keeping with that amount of klm's on the clock. they just go forever.