Filling the bike up

 

I went to a gas station and started pumping the nice swedishly
priced gas at $6 per gallon. As i was doing that, i tried to fill
her up "to the edges" so to speak. To my surprise, as the level
reached the edges and i released the pump handle, the level
slowly dropped an inch or so.

Well, i though, just as well as to put in some more. As i did it,
the level dropped again. I've done that four times and then
got scared that there was a leak somewhere. There wasn't
any, though.

So, i have two questions now.
1. How can that happen and is it a common behavior?
2. Is it recommended not to fill the bike up to the edges?

I have a Varadero 2003, if it's of any relevance.

--
Vänligen
Konrad
---------------------------------------------------

Sleep - thing used by ineffective people
            as a substitute for coffee

Ambition - a poor excuse for not having
                 enough sence to be lazy
---------------------------------------------------

 

Konrad Viltersten wrote:


My guess is your bike has a filler neck that extends downwards,
something like this:

http://www.freepatentsonline.com/20030042261-0-display.jpg
(imagine part "102" not being sealed at the bottom).

 > and is it a common behavior?

Probably; all my "modern" bikes all have this feature;
the older ones don't.


Yes. My Suzuki S40 owner's manual says:

   ! WARNING
   Overfilling the fuel tank can cause
   the fuel to overflow when it expands
   due to heat from the engine or the sun.
   Spilled fuel can catch on fire.

   Never fill the fuel above the bottom
   of the filler neck.

Sean_Q_

 


The gas tank air venting system was working. Trapped air was escaping
and gasoline was taking the place of the air and the fuel level in the
gas tank readjusted itself.

If you study the evaporative control system  (or the fuel tank vent
system, if there is no charcoal canister) you may learn something
about your motorcycle.

There is probably a mysterious-looking decal under the side cover, or
under the gas tank that shows the routing of all the fuel tank vent
hoses and evaporative control system.

Motorcycle manufacturers warn against filling a gas tank to the top,
since gasoline evaporates when the motorcycle sits in the hot sun and
that will pressurize the gas tank and gasoline will escape and cause a
fire hazard or air pollution.

In modern countries, where the authorities are concerned about the
health risks of air pollution, motor vehicles must have an evaporative
control system to dispose of the fumes from evaporating gasoline.

Modern motorcycle gas tanks are designed with a filler neck that
extends into the tank about 50 millimeters. If you fill the tank and
the gasoline level rises into the filler neck, you've created a liquid
barrier to the escape of the air in the top of the tank

When you fill the fuel tank with gasoline, the air inside has to
find a way to equalize pressure with the air outside the tank.

Some early motorcycles with filler necks had a vent tube on the front
of the gas tank and the rubber vent hose went up and then was routed
down through the steering spindle.

That made the motorcycle look like a racer.

Later designs have a steel vent tube that starts inside the gas tank,
up in the air bubble above the gasoline. Then the steel vent tube goes
down through the gas tank to the rear of the tank and a rubber vent
hose carries the air and gasoline fumes directly to the inlet port
downstream of the carburetor or to a charcoal canister and then to the
inlet port downstream of the throttle butterfly.

Does your Varadero have a charcoal canister for collecting gasoline
vapors?

Charcoal canisters are intended to only store gasoline fumes, there is
no direct vent to the atmosphere. If you overfill the gas tank, the
charcoal canister can be flooded with gasoline and some of the
gasoline will drip out the bottom of the canister.
The engine won't run smoothly until it can suck all the fumes out of
the canister. If the engine sucks raw fuel back out of the canister,
it will flood out and stall.

Normally, when you start the engine, only gasoline fumes are sucked
into the inlet port downstream of the carburetor and burned. There is
a one-way ball check valve in the rubber hose to prevent backfires
from igniting vapors in this evaporative control system.

 

Morrgaine wrote/skrev/kaita/popisal/schreibt :


<snip>

I'm guessing so, since it doesn't have a carburator, i've been
told. On the other hand, i've been told so in swedish which
might gave rise to misunderstandings due to my limited
eloquency regarding technical terms. Carburator is the thing
one had before fules injectors were installed, right?

--
Vänligen
Konrad
---------------------------------------------------

Sleep - thing used by ineffective people
            as a substitute for coffee

Ambition - a poor excuse for not having
                 enough sence to be lazy
---------------------------------------------------

 


Yes, carburetors were used before fuel injector became more
commonly used. But your gas tank still needs an air venting system and
possibly has a characoal canister to absorb gasoline fumes.

If it does have a canister, it can be mounted in front of the engine,
behind it, between the cylinders, or any place you can imagine.

A charcoal canister may be round, or it may be shaped like a box. The
canister used on a Transalp looked like this:

http://houseofmotorcycles.bikebandit.com/parts/Honda/XL600V+TRANSALP/1989/176759

The phenomenon of changing fuel levels in your gas tank as you fill it
doesn't necessarily point to any problem, as long as you don't over
fill the tank and temporarily flood the canister.