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'87 K100RT My Flying Brick Stinks! Why?

Paul_F

RK Ryder
Last year I exclusively rode my K in the spring but then parked in on the bike lift, on the side stand until mid-September. Sort of forgot about it because my R was running so smoothly.

So when I finally got back on the K, it would stink of gasoline for maybe the first thirty minutes before the air would clear. Even ran the tank quite empty a couple of times and refilled it with fresh ethanol free gas. Always the same, smelly gasoline odour for the first 30 minutes or so of the ride. Parked it for the winter on its' centre stand with fresh ethanol free gasoline in the tank.

Took it out today for the first ride of the season (with 267,00 km on the odometre). Same smell for the first part of the ride. No odours when returned home.

Can anyone suggest where the problem might lie? :scratch
 
The classic K bikes originally had vent and drain lines from the tank to the right foot peg area. Then a rectangular funnel device (called an air accumulator) was used to place beneath the drain and vent stub pipes on the tank with a single hose down to the right foot peg area. On my several K75s this has caused fuel odors as you have described because the tank vent is open to the atmosphere at waist level instead of below ankle level. This may be what you are encountering. Raise the rear of the tank and see if you have the air accumulator and if not, see if the vent hose is attached to the stub pipe on the tank.
 
Sounds like a fuel line leak or loose clamp.

The classic K bikes originally had vent and drain lines from the tank to the right foot peg area. Then a rectangular funnel device (called an air accumulator) was used to place beneath the drain and vent stub pipes on the tank with a single hose down to the right foot peg area. On my several K75s this has caused fuel odors as you have described because the tank vent is open to the atmosphere at waist level instead of below ankle level. This may be what you are encountering. Raise the rear of the tank and see if you have the air accumulator and if not, see if the vent hose is attached to the stub pipe on the tank.

Thank you for these suggestions.

Today will not work for looking at the K but I will look at it this week. The gas tank was off in the winter of 2018 and although I don't recall a gasoline fumes in the spring of '18, I really did not ride the bike much until the fall. Possibly I did not put the tank back on correctly or tighten the hose clamp properly.
 
I just looked at the bike and no vent hose is visible hanging on the right side!!!

When look into the bike more closely and discover that my vent hose has vanished, must I have BMW OEM hose or can a local auto parts store supply an equivalent. If so what characteristics must the hose have?
 
I think any gasoline rated hose of the correct diameter would be fine.

Take the collection cup with you and find something that fits correctly.
 
I just looked at the bike and no vent hose is visible hanging on the right side!!!

When look into the bike more closely and discover that my vent hose has vanished, must I have BMW OEM hose or can a local auto parts store supply an equivalent. If so what characteristics must the hose have?

Most of the fuel or vacuum line sold at auto parts stores is fairly thick-walled, thus harder to route than it needs to be. If you don’t want to buy BMW tubing, which is thinner-walled, determine the ID you want then do a search on Amazon for “rubber tubing”. You’ll find a variety of sizes, lengths, etc. so pick the ID you need. Lots of options in 1/16” wall tubing, which is plenty heavy enough for your vent line. Beyond that, try to get a fuel-rated version but I wouldn’t stress over that part too much on an atmospheric vent line. Age, heat, and atmospheric ozone will destroy it as much or more than fuel fumes.

Best,
DG
 
Paul,

Please remember to include the year and model of the bike IN THE TITLE of your thread. I've added it for you this time.

Thanks.




:dance:dance:dance
 
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I'd also take a look the seals in/around your gas cap - they aren't getting any younger...

Bob's BMW has a rebuild kit (you have to call, as it's not listed on their website) and Chris Harris has a Youtube video on how to refresh the seals.
 
The bikes that didn't come with "the cup" (air accumulator) had the tank vented to the crankcase.

The tank vent is the forward nipple underneath the tank about 7" from the rear of the tank just to the right of the centerline. The vent hose runs forward, through a check valve, to a nipple on top of the front of the block just below the fan. Most US smog spec. bikes are vented this way.




:dance:dance:dance
 
The bikes that didn't come with "the cup" (air accumulator) had the tank vented to the crankcase.

The tank vent is the forward nipple underneath the tank about 7" from the rear of the tank just to the right of the centerline. The vent hose runs forward, through a check valve, to a nipple on top of the front of the block just below the fan. Most US smog spec. bikes are vented this way.




:dance:dance:dance

When I bought my K75T in 1986 the dealer re-routed the vent away from the crankcase at the 600 mile service. The issue was/is that if the tank were to be overfilled, or even if not, if left sitting in the hot sun right after a fillup, it can puke raw gas into the crankcase and dilute the oil. If you have one still vented to the crankcase I would cap the stub pipe at the engine and add an air accumulator (little square funnel) or just run the vent line to the right footpeg area.
 
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I have changed all 6 of my K75Ss over to the cup and I change every bike I work on over.

I find about half the bikes that come in for the first time have nothing, no cup and a disconnected hose to the crankcase(which creates a vacuum leak and lean mixture).




:dance:dance:dance
 
You should also take a peek at the rubber o-ring/gasket that is between the tank and the fuel level indicator. I've had to replace a couple. In my experience, you won't get a "leak" - more like a drop or two that spreads itself out on the top of the electrical box.

It's a very easy fix.

- Take the tank off (after you have drained it)
- Flip upside down
- Undo the 4 screws
- Gently lift the fuel level indicator, being careful not to bend the float
- Renew the o-ring and put everything back together
 
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