Stihl FS-85 leaking fuel when stored vertical?

Yesterday, I hung it in the garage like normal [1] and a few hours later the garage was filled with the unmistakable odor of gasoline. On closer inspection, I found some gas/oil splatters on the wall. Definitely came from the FS85.

The splatter pattern on the wall suggested a fairly fine spray, not large drops like a drip and it was on the side with the gas cap and fuel lines.

I didn't notice the fuel level when I hung it up but since I only filled the tank about halfway for the job, it couldn't have been more than 1/4 to 1/3 full when I finished...definitely below the gas cap. Now, the gas cap does have a vent hole but it's pointing away from the wall. If the gas did somehow spew through the hole, I'd think the splatters would be on the garage floor, not the wall.

After cleaning the wall, I left it horizontally on the floor overnight. No additional gas leakage and no odor.

I need to take the cover off and give the engine and tank area a good cleaning so that I can tell where the gas is spewing. But I was hoping someone else has experienced this and could give some clues about what's going on. Should the FS85 not be stored vertically when there's fuel in the tank?

[1] Being paranoid, after using it I always let it cool off on the driveway for a couple hours before storing it on its hook.

 

The only thing that comes to my mind is a crack/slit in one of the fuel/primer lines or in the primer bulb.

 

Sorry about the late response. I got busy with other things and forgot about the Stihl's problem until today. Haven't used it since my original post. In the meantime, I'd been storing it horizontally on the garage floor. No leaks or gas smell until today.

Yesterday I bumped the trimmer with my foot causing it to rock back and forth a couple times. Today, there was some gas on top of the tank just beneath the carb. Looks like it's dripping down from the throttle and onto the low idle adjust screw. Not sure if the throttle is the culprit or if it's leaking from somewhere else down onto the throttle. The fuel lines themselves appear to be intact.

 

Could be a leak in the primer bulb, a carb gasket, a leaking needle (which would probably just leak into the carb throat), or fuel line (tiny pinhole).

 

Thanks for the insight. I'll replace the lines and the primer bulb and see if that solves the problem. The bulb HAS lost some of its "springiness" so it should probably be replaced even if it's not the cause of the leak.

 

Okay. Replaced the bulb, fuel lines and figured while I was at it , I'd clean the carb and install a zama carb kit. Then I used it for about 30 minutes around the yard (she started on first pull). Then left it sitting horizontally on my garage floor. It was there for over a week with no leaks[1].

Fast forward to today. Today was a fairly warm day (~80F) compared to the last week and since the garage was closed-up, it got pretty warm in there. I'd guess maybe 85-90F. When I came home from work, I noticed a gas smell and sure enough, a paper towel dobbed on the underside of the carb came away with a fair amount of gas. So it looks like it's still leaking.

Since it was good for a week, I'm thinking maybe the temperature is a clue? Is it possible that the temperature is causing pressure to build in the gas tank when in turn is forcing the needle out?

Failing that, is it possible that the throttle shaft has somehow become worn and is leaking? The carb kit didin't come with any seals for the shaft so I assume it's a part that doesn't often fail?

[1] That's not entirely true. The new fuel line is apparently a little smaller than the OEM stuff so they don't fit the fuel tank grommets as tightly and so you can see some gas slowly seep up through the grommets. I'll replace the grommets this weekend. It'd be nice if this is the problem but it doesn't really explain how the gas is getting onto the bottom of the carb unless the gas is "spraying" upwards from the tank.

 

The throttle shaft shouldn't allow a leak even if it was worn. (not a fuel leak anyway). Gas has virtually no surface tension, so it can creep upwards. Maybe it is creeping up towards the carb? Not all that likely I guess, but I'd fix the leak at the grommet and see what happens. Barring that, you may still have a leaking gasket at the carb for some reason, possibly some varnish or something on the needle seat.