Tank leaks when full from cap?

[nzspokes]

If I fill my bike up and not ride it there is petrol leaking out of the cap. So does this mean the cap is not venting properly?

[avgas]

Yep. I had similar prob with an SRX. Gave the cap and its seat a good clean out and its came right.
The only other time I have seen it is the bright sparks that fill their bike by standing it up (aka sit on the seat) then put it on the side stand to go pay.............only to come back and see that extra 100ml of gas they put in, has either tipped out the vent or the overflow.

[nzspokes]

My bike has no external vent for the tank, so guessing it does so through the cap. Wondering if it could be partially blocked. Petrol seems to come out the key hole. If so it wouldnt be helping my top end power.

Only happens when its hot. Last time I lifted the cap off and a bubble came up from the bottom of the tank.

[FJRider]

If I fill my bike up and not ride it there is petrol leaking out of the cap. So does this mean the cap is not venting properly?

Petrol in the tanks of fuel stations is cold ... put it in a motorcycle fuel tank in the sun, the petrol will warm up. As it does so ... it will expand. Either through the overflow, or the fuel cap. Whichever is the easiest path.

Even the roadside camber can cause an overflow with a full tank.

If you are leaving a bike parked after refuelling ... dont fill it completely full ...

[nzspokes]

Petrol in the tanks of fuel stations is cold ... put it in a motorcycle fuel tank in the sun, the petrol will warm up. As it does so ... it will expand. Either through the overflow, or the fuel cap. Whichever is the easiest path.

Even the roadside camber can cause an overflow with a full tank.

If you are leaving a bike parked after refuelling ... dont fill it completely full ...

That is what I had been doing but got caught out last weekend after someone took a bit long than expected to arrive at a meeting point.

May just pull the cap apart anyway. But wont fill up before parking.

Thinking of making a tank cover which may keep it a bit cooler to.

[FJRider]

May just pull the cap apart anyway. But wont fill up before parking.

Why ... ??? if petrol can get OUT ... AIR can get IN ...

Most vents on fuel caps on older bikes, are small holes in the metal part, that are not aligned with a hole in the cap liner ...

This acts as more of a splash guard ... rather than as a vent ... as such.

[nzspokes]

Why ... ??? if petrol can get OUT ... AIR can get IN ...

Agreed, but if one of the holes is partially blocked then tank may not be venting correctly. Worth a 5 min look.

[FJRider]

Agreed, but if one of the holes is partially blocked then tank may not be venting correctly. Worth a 5 min look.

First check it has not got an overflow ... that is blocked ...

[nzspokes]

First check it has not got an overflow ... that is blocked ...

Will do. But not seen one yet.

[Gremlin]

Tanks should have an overflow... but I know bugger all about older bikes.

As FJRider says... fuel expands in the heat, so if you're filling all the way to the top, then leaving it standing still, the fuel has to go somewhere...

[sinfull]

A previous owner probably saw fuel leaking out the overflow under the bike under similar circumstances and plugged it lol

That'll fix it, yeah right !

[TrentNz]

wrap some thread tape (the stuff plumbers use, forgot the real name) around the thread. that should stop it leaking

[caseye]

Have had an old XV for over 5 years, two years ago I took her off the road and rebuilt her from the crankcase up and all parts in between and above.
She looks beautiful. 4 Months ago I got her back on the road. I took her out one Saturday, got home, filled up next door,(handy having a gassey next door) and parked her up in the shed.
Came out on Sunday morning hopped on board and headed off to the FBMC \'s Waiheke TT memorial run.
Got half way there looked down and saw lines in my tank.
People I've owned this bike for over 5 years, never once had a fuel issue.
Butt this one time I must have put too much in the tank and she had no way out except the filler cap, had run all night out of the cap and down over the entire rear of the tank, destroyed my custom paint job on both the tank and the left hand side cover.
Took another 4 months to get her sorted and back on the road.
Happy to report she is now alive and well and turning heads everywhere she goes.
Point is, be bloody careful and if your tank has a breather, make sure it works, if as in most older bikes it has a hole bored in the spring mechanism under the cap, then check that it is not filled with crap and also works.
Make sure of these things and please don't experience the heart ache and loss that I have.

[Tigadee]

Only happens when its hot. Last time I lifted the cap off and a bubble came up from the bottom of the tank.

That must have been an interesting sight...

[nzspokes]

That must have been an interesting sight...

Petrol fart.

Another problem with tanks but on my new bike today. Left it sitting in the sun. Wore shorts today at lunch time to pop out. Black tank left in sun and bare knees dont play together nice.