Gas boils over during fill up.

[Anonymous]

I’ve got one that really has me thinking.

Occasionally when filling my 1978 GS 1000 with gas, it seems to boil over. I actually see the gas in the tank rising to a point when the gas is overflowing and drop as soon as what seems to me a large air pocket emerge from the tank. This doesn’t only happen once it could happen a few times per fill up. Actually there are time’s when I think it’s done, I park the bike go away for a coffee and when I return there is a huge puddle of gas under the old girl. It’s almost as if the gas is being siphoned out of the tank. This only seems to happen after I have been riding for a few hours.

I’ve tapped the side of the tank during fill ups and this seems to help a bit, not much but a bit.

I mentioned this to Tim White during a group ride and he mentioned it could be that the vacuum/petcock is somehow causing this. Any ideas.

Roman

[mcconnell]

Is your gas coming out of the gas cap? Did you or someone put a liner (Kreem) in the tank? In the filler neck is a small vent to the air pocket in the top of the tank. If this vent hole is blocked, as the fuel expands due to the hot engine underneath the tank, all expansion has to take place in the small volume of the filler neck. I learned this by coating my tank and blocking this hole. I, too, ended up with a lot of gas on the floor.

[Anonymous]

Is your gas coming out of the gas cap? Did you or someone put a liner (Kreem) in the tank? In the filler neck is a small vent to the air pocket in the top of the tank. If this vent hole is blocked, as the fuel expands due to the hot engine underneath the tank, all expansion has to take place in the small volume of the filler neck. I learned this by coating my tank and blocking this hole. I, too, ended up with a lot of gas on the floor.

Yes it is coming out of the gas cap, I never thought of this. I'll check for the vent hole and it's condition later on tonight when I get home and my kids get to bed.

Is the vent hole in an obvious spot?

Thanks

Roman.

[mcconnell]

Take off the gas cap and look down the filler neck. The hole should be obvious. If memory serves, it is on the right side about 1/2" to 1" down the neck. Good luck.

[Anonymous]

Thanks I'll give it a shot.

Roman

[KEITH KRAUSE]

Is your gas coming out of the gas cap? Did you or someone put a liner (Kreem) in the tank? In the filler neck is a small vent to the air pocket in the top of the tank. If this vent hole is blocked, as the fuel expands due to the hot engine underneath the tank, all expansion has to take place in the small volume of the filler neck. I learned this by coating my tank and blocking this hole. I, too, ended up with a lot of gas on the floor.

Yes it is coming out of the gas cap, I never thought of this. I'll check for the vent hole and it's condition later on tonight when I get home and my kids get to bed.

Is the vent hole in an obvious spot?

Thanks

Roman.

Hi Roman. I just looked inside my '79 1000 tank. When sitting on the bike, the tank vent hole is just inside the right side notch/cut-out for the gas cap. You should also clean the vent in the gas cap itself. The cavity with the ball rattling around. If you use carb spray, rinse it off with gas immediately. The carb spray cleans good but is bad for the rubber gasket.
I Kreemed my tank years ago and almost forgot to clear the vent hole.

[Anonymous]

Thanks guys I'll take a look tonight. I hope it’s as easy as that.

Roman.

[saaz]

The standard vent hole is on the small side, making it tricky to fill the tank right the way to the top. Beware filling the tank right to the top unless you are riding off straight away (after paying the the petrol of course!). The motor heat will expanding the petrol, making it spill. If you want it really full, do it as you are about to leave.

[Anonymous]

In an effort to extend my range as far as possible I always try to defeat the filler neck, dripping it in slowly until the tank has had a chance to vent for maximum fill. But as saaz says, you better be making use of that last half gallon soon, because the fuel from those underground tanks is quite cold, and the expansion possible on a hot day will amaze you. First time it happened I thought the tank was leaking. Second time I put 2+2 together. Those spillovers look like the tank emptied onto the parking lot, but it ws stil "full".

[saaz]

If you really want to fill quicker, make the breather hole on the neck bigger. This was covered in the last few weeks.

[Anonymous]

Well Gang I found the small hole, and yes it was covered with something.
What really surprised me was how small this thing is.

Tanks for your help. :roll: :roll:
Roman