fuel tank vacuum

[momagic]

I'm sure I've read something about this years ago but as ever can't find it when you need it. 1150GS, serviced two weeks ago, just done 1100 miles running up to Stornoway and back, and every time I go to open the fuel filler cap it's a bugger to open - there's a vacuum forming. Rode back down with the fuel cap open (covered by a paper towel and a Baglux bag). Have tried blowing up the breather pipe - it's definitely blocked (the other pipe for the fuel-filler water run off is OK). Part lifting the tank shows the pipe run seems to be OK with no snags so I assume some debris has gone in during the tank removal at service. Have tried forcing more air up the pipe with a more powerful 'stand-up' style bicycle pump but it just blows off the at the connector. So what next? Any advice welcome. Thanks. Mark.

 

[Brian V]

I had a similar prob with my 1100 about three years ago. Same symptoms, In the end I had to change the entire inner filler neck assembly 'cos the steel breather pipe had split where it's brazed/welded to the inner neck. Your problem may, as you say may just be a blocked breather but check the inner filler neck just in case.
Also you don't say what year your 1150 is or how many miles it's done. The 1100 was a '98 with about 100k at the time


KRBV

 

[momagic]

Thanks Brian - though sounds ominous. My bike's a 2000 'W" but only done 16000 miles. I do about about 3k a year now and that's mostly in three or four big trips rather than frequent runs so possibly a corrosion problem through lack of use. Will investigate. Mark

 

[B Murr]

I had a similar problem with my car( audi a4). Major vacuum forming in the tank such that I feared it would implode, hissing noise was the giveaway. I replaced cap thinking it was a blocked cap. No difference. Eventually I figured that the car has a fuel evaporative control sytem which basically ensures that the tank never has a positive pressure which could release fuel vapours into athmosphere, the excess vapours are taken to the engines air intake via a charcoal filter and burnt in the cylinders. When this system opoerates correctly the vacuum is generated by the air intake of the engine but crucially it is controlled by a solenoid valve. My vsolenoid had stuck in the open position thereby creating excess vacuum. Is it possible that such a system operates on these bikes?? If no then I have of course been bugger all help to you