K75RT Strong Gas Odor (but not always)

[cookiemech]

1994 K75RT, 88K miles, Owned since 2003, 100% of all service done by me.

If I have not ridden the bike for, say, a couple of weeks or more (have several other bikes), then the first time I ride it, there is a strong, almost overpowering raw gasoline odor that can last for 10 or more miles. At some point it stops and does not return until the next layup period. For example, yesterday morning early it was 37°F and raining, so it was the weapon of choice to visit my dentist, 20 miles away. Sickening fumes for a bit over half the trip, then it subsided. On the return trip, no fumes.

Today was a very similar early day trip to almost exactly the same place. Near identical weather conditions. No fumes at all.

At all times, bike starts easily, runs well, idles well.

I've rebuilt the gas cap with new seals, pulled the injectors, cleaned them externally and replaced the o-rings. Ran some BG fuel system conditioner. Bike always has fairly fresh Top Tier gas in it.

Of course I have always performed all maintenance by the book. No neglect.

Love to hear suggestions. If there were a leak, it couldn't heal itself.

[The Mighty Gryphon]

Welcome! 

The first question that comes to mind is whether or not a close inspection before riding reveals this gasoline odor before the engine is started.  If so, I would suspect that there will be an amount of fuel pooled on the top of the crankcase.  Finding that puddle of gasoline would go a long way toward finding the source of the leak.  Having the strong odor for ten minutes tells me that the amount of leakage is not insignificant and should be easy to find if it is present.  However, it would require removong the fairing lowers to really be able to see the top of the block.

The other source of the odor may be fuel that has collected in the exhaust system.  This may be the result of an injector not sealing completely when de energized.  If it takes a couple weeks to get enough to smell, the leak is going to be pretty small and hard to spot. 

The only test that comes to mind is removing the injectors and the rail as a unit after shutting down the engine and then letting the injectors hang, with some sort of containers to catch what they leak.  Then leave them hanging for a week or two and see if, and how much each one has leaked.  I would expect the amount will be less than an ounce. 

You might want to clean the engine well and, after removing the fairing lowers, dust the block and all the areas close to fuel lines and the injectors with talcum powder.  Any leaks will be glaringly obvious against the white of the powder.  When you are done the powder is easy to wash away.

[cookiemech]

First question is easy to answer. No particular gasoline odor before startup.

I can certainly pull the rail to see if it drips after shutdown. Could enough gas pool in the exhaust system to stink (horribly) for 10 miles? I realize the RT cockpit is a dead air zone (making it the ideal cold weather bike).

[frankenduck]

A K bike gas tank has two vent pipes at the right rear of it.



The rear one drains water that accumulates around the gas cap when it's raining. It drains water from the left side of the gas cap. The rear one had a hose attached that emptied the water out near the back of the right peg plate.




The front one vents gas fumes from the tank. The original design (to make California happy) had a tube with a check valve that sent the fumes down to a pipe at the front of the engine.




At some point BMW came out with "the cup." (Part 16132307467 - Air accumulator) It sits in the frame under those two pipes and drains out to a hose behind the right peg plate. (If the cup was used then a cap was put on the pipe at the front of the engine.)





(I added the zip-ties to keep it in place.)

If your K75RT has the cup then as the gas and fumes in your tank warm up and expand when you start riding then fumes come out of that front pipe and get trapped in air bubble behind the RT fairing.

[frankenduck]

To stop the odor you could attach hoses to both pipes and have both of them run down to the right peg plate.

[cookiemech]

Sure, I have had the "air accumulator" on this bike (and my naked K75) for many years. But why would this setup start causing a problem with gas fumes much later (and more importantly, only after the bike sits for a long while)?

I had the same batch of gasoline in the tank yesterday and today, though yesterday morning the tank was more full (maybe only 32 miles or so since fill-up). However, there was no fume problem on the day I filled the tank, two or three weeks ago.

[frankenduck]

There's a vapor collector "burrito" in front of the gas cap. Perhaps more gas fumes or more dense fumes collect in that when a bike sits for a while.

[Laitch]

I've rebuilt the gas cap with new seals, pulled the injectors, cleaned them externally and replaced the o-rings. Ran some BG fuel system conditioner.

Did you do these procedures after the fuel odors started, or before?

[cookiemech]

Did you do these procedures after the fuel odors started, or before?

After.

Today I FINALLY solved the problem!

I don't ride the bike in warm weather, and it's been sitting on my lift table, waiting for a crappy weather day, which happened today. I planned to remove the tank and maybe replace the level sender O-ring. And maybe try to see if any injectors were leaking. So I pulled the lower left-side fairing, which I had to do to remove the fuel lines to the tank. I thought that it might be good to start the bike and look closely at the injectors. Maybe a crack or bad O-ring on one?

Fired it up. Nope, injectors were nice and dry. What wasn't nice and dry was the junction of the tank nipple and the pressure hose (from the pump). Gas was bubbling out and dribbling down the hose.

Shut it down and pulled the hose. The clamp was tight, but not TIGHT. Examined both hose and nipple with a bright light and mirror (for the nipple). No cracks, and the hose was reasonably soft. Reassembled, pushing the hose on as far as possible (maybe 1 mm further than before). Carefully positioned the clamp and made it TIGHT. Started up, and no more leak. Shut down and waited a while. Nice and dry.

I just don't understand why it would apparently "heal" itself after 20 miles or so, or if I rode it every day. If it always stank of gas, I would have jumped on a "leak" diagnosis immediately.

Thanks for the help!

[Laitch]

Tight but not tight and reasonably soft aren't useful descriptors. Is a fuel injection hose clamp being used or a jubilee clamp? The hose could have been shrinking when dry and swelling when soaked and warm. Couple that circumstance with a clamp that isn't tight enough, and there you go.

Consider replacing that hose, or taking the win and moving on. 

[cookiemech]

It's the original FI clamp. I'll be replacing the fuel hose next time I place an order. Need a $99 order now with MAX for "free" shipping.

[Laitch]

Sometimes only a small amount of torque is the difference between success and failure. You did well to persist until success. Maybe this fixes things. Buy yourself some M&Ms.