Is This Normal? Gas tank builds pressure and contracts.

[Air_Head_Ed]

Newbie here. My '94 R1100RS gas tank contracts and expands. Is This Normal?!

I can visibly see a gap between the gas tank and fairing. When I open the gas fill lid

I can hear the tank depressurize and the tank will expand.

What's up with that?

[dirtrider]

18 minutes ago, Air_Head_Ed said:

Newbie here. My '94 R1100RS gas tank contracts and expands. Is This Normal?!

I can visibly see a gap between the gas tank and fairing. When I open the gas fill lid

I can hear the tank depressurize and the tank will expand.

What's up with that?

 

Evening Air_Head_Ed   

 

Not normal, sounds like you have a plugged tank vent.

 

Could be a plugged up evap can (if your bike has one), or an incorrectly connected tank vent hose, or a pinched vent hose. (something not allowing the  fuel tank to vent correctly)

 

In any case you need to find the problem & repair it as  you can damage your fuel gauge sensor.

 

I don't think that your tank is pressurizing but instead it's probably going to  negative pressure (vacuum).   As the fuel is used out of the tank no air can get in to replace the used fuel so it goes negative pressure inside the tank then sucks the tank sides in.

[Air_Head_Ed]

D.R.,  Thank you! I'm glad it's not normal and will have it checked out soon.

[SAS]

Agreed negative pressure.  Mine did the same thing.  Evap canister was clogged, not allowing the tank to vent as fuel is being used.  Sounds like you need to do a canisterectomy. 

[Air_Head_Ed]

The previous owner has already eliminated the evap canister. Gonna have to do some digging.  Thanks

[dirtrider]

13 hours ago, Air_Head_Ed said:

D.R.,  Thank you! I'm glad it's not normal and will have it checked out soon.

 

Morning Air_Head_Ed   

 

There were 3 hoses going into that removed Evap can, one coming from the fuel tank vent, one going to atmosphere behind the R/H riders foot peg & one going to the purge solenoid on L/H side of motorcycle about mid frame area.

 

To by-pass that emission canister  they probably hooked the hose coming from the fuel tank  to the one  running to the behind the riders R/H foot peg then simply plugged off the remaining hose going to the L/H side purge solenoid. (or possibly they removed the entire purge solenoid & hoses then plugged it off at the throttle body nipples).

 

The bottom  (exit) of the hose that exits behind the riders foot peg should be cut to a 45° angle to prevent  water from being sucked back into the fuel tank, or prevent dirt from  plugging the hose.

 

If the removed canister was severely plugged up inside then some of that goo might have been sucked into the vent hoses & plugged them up.

 

The internal tank vent vents down through the inside of the fuel tank   then out though the fuel pump pass-through (small metal fitting through the pass-through plate), they sometimes plug in that little pass-through pipe area.

 

Open the fuel cap, then  find the vent hose behind the riders R/H foot peg, then blow into that hose to see if you can hear air escaping out of the filler cap area.

 

It's also possible that whoever removed the evap can didn't so it correctly.   (you probably should check the hose routing & connections).

 

Just to make you aware, there are two smaller hoses coming from the fuel tank pass-through. One is the tank vent mentioned above & the other is a drain hose coming from the fuel tank filler neck filler area (don't get them confused).

 

 

[dan cata]

19 hours ago, dirtrider said:

 

 

 

Open the fuel cap, then  find the vent hose behind the riders R/H foot peg, then blow into that hose to see if you can hear air escaping out of the filler cap area.

 

 

+1!

 

Dan.

[cat0020]

My 07 R1200S does something similar, fuel cap is difficult to open once I ride 100+ miles.. some major suction keeps the fuel cap shut.. usually take a few seconds for air to slowly leak into the tank with fuel cap key turned. 

[dirtrider]

7 minutes ago, cat0020 said:

My 07 R1200S does something similar, fuel cap is difficult to open once I ride 100+ miles.. some major suction keeps the fuel cap shut.. usually take a few seconds for air to slowly leak into the tank with fuel cap key turned. 

 

Morning  cat0020

 

Then you also have fuel tank venting problem. Make sure that your fuel tank is vented correctly & nothing is plugged or incorrectly connected.  

[Lowndes]

If you're in the South, you can/will get dirt daubers, a type of wasp,  building their nests in the end of any tube or small hole. There can be several layers of larvae and various insects for the larvae to feed on, all separated by plugs of dried mud carried in by mama wasp.  They will find any and every tube and hole.  Our tubes are prime real estate.

[SAS]

cat0020

Do you still have your canister installed and hooked up?

[cat0020]

6 hours ago, SAS said:

cat0020

Do you still have your canister installed and hooked up?

 

Nope, those were long gone.