vacuum in gas tank

My gas tank isn't venting. When I open the cap there is a vacuum inside the tank and it is hard to open the cap. When it opens I hear air rushing into the tank. I have raised the tank and there were no kinks in the hoses. Any suggestions? I have limited tools with me as I am on a trip.

That is just the fuel returning to the gas tank from the fuel pump and fuels lines. That is normal operation for an ST in warm weather.

I don't think this is normal... I can barely get the cap open... Is there a vent on the gas cap itself? It has never done this before. After 50 or so miles me FIlight comes on... I stop and open the cap and when I restart I can go another 50 and the FI light comes on again.

In Arizona we have a little bug that likes to fill the drain hoses with leaves. You know he's been around when you take a corner in your car, and all the condensation off the AC runs out onto your legs. To cure it, we blow out the hose with a little compressed air.
Have you tried that to see if the vent line for the tank might be blocked?

Are you talking about the vent line that comes out of the bike on the bottom of the faring near the left footpeg?

1st thing is to see what the FI light is telling you - how many blinks?

Yes, there's a vend hose and it sometimes get's bent but if it's old it may just not have any internal structure to it and look okay but collapse some with pressure and it may be clogged as well.

The cap itself isn't vented that I'm aware of.

Randy, see attached schematics.

In the Fuel Tank image, tube 6 drains the space under the fuel cap but exterior to the fuel tank (where water can collect in rainstorms or where fuel is spilled outside of the neck of the fuel tank). It drains directly under the middle of the bike (is an uninterrupted line). This tube is not the issue.

In the Fuel Tank image, tube 7 is called a 'breather tube' and it is likely plugged or kinked, other downstream lines are plugged. Follow that connection onto the Evap Canister image and you'll see it attached to a more complex series of lines and into the canister itself. If fuel gets sucked into that canister and the fuel doesn't drain through tube 10, there can be a hydraulic lock and your tank will pull a vacuum as the fuel is used. Check the vent line 9 and both drain lines 10 and 13 to make sure they're not plugged or kinked. You may also want to check lines 3 and 11 to make sure they're not plugged or kinked (and potentially purge control solenoid valve #6 electrical operation). Line 11 on the Evap Canister image connects into the Throttle Body Assy image at the 5-way tee (part #5). It's a maze for emissions control.

I'm back from the trip and here's what I found on the 2nd day... I raised the tank and pulled the breather tube loose and for sure, it was plugged. I couldn't get the obstruction out, so I disconnected the tube at a plastic connector about a foot from the tank and this was far enough up the tube that there was no obstruction. As far as the FI light coming on, it happens when the engine passes 4000 rpm and doesn't affect performance at all. I checked for the code and I got 2 long and 6 short blinks. I think that might be a knock sensor, but as I just got back, I haven't had a chance to check it out.

had the same issue a couple of years ago: the problem was due to the venting pipes of the lower tank, which are running on the back of the upper tank and going to the fuel cap. Simply the pipes were clamped between the tank and the airbox. Raised the tank, moved the pipes in the correct position and solved the problem.

Gents
I know this is an old thread but it appears my riding buddy is having similar issues and I ride a 1100 so having stabs in the dark. The issue is full tank and ride for 100 miles (160km in Aust) and the bike looses power and stops. This is pretty consistent with amount of fuel used and distance traveled. Opening the fuel cap can not hear air rushing in but the cap is reasonably hard to open as if held. Bike runs fine for another 20miles then stalls completely. Open tank and ride with cap open for 5 miles then bike misses and stalls.
We eventually get home and strip plastic etc. The vent pipes are clean and open (no kinks) and no charcoal canister on bike. 5 way clean and has been cleaned before. No F1 indicator light at all. I have a new fuel pump ready but have been holding off as it does not appear to be the problem.
So thoughts are; 1. something is shorting out at that level of fuel 3 bars. The only thing electrical is the fuel level float for the top tank.
2. Fuel pump problem
3. Coils heating up over a long time and shorting.

Any suggestions are welcome because I don't want to pull this thing apart too many more times!
Happy miles from Western Australia

To me this sounds like typical fuel pump problem, will be watching tread to see outcome.