Can anyone explain how the tank fuelling works?

[GrinningGSer]

I have studied parts fiches and am unable to understand the tankfuelling:

Where does the fuel pump suck its fuel from? The lower drawing shows two tubes and do they each suck from the lowest point on each side of the tank?

My reason for asking, is that my bike, with 1 gallon of fuel, would not start yesterday after being on its right hand side during an offroad drop. We needed to lean it to the left and then it started as normal?

Any explanations from the learned masses appreciated.

 

[GrinningGSer]

27 views and no answers. I have either asked a really dumb queston or 27 voyeurs do not know the answer

 

[trainman]

haynes book says there is a 'balance pump' that feeds fuel from RH side of tank to LH side (GS only)

i have never seen this pump mentioned on the forum and on the electrical scheme in the book the only pump shown is the main fuel pump - what this balance pump is and how it is powered i dont know (the manual does not describe where it is exactly or how to test/change it)

i guess it could be some sort of vacuum jobbie maybe?

 

[TeaPig]

Normal riding sloshes tank around the tank. If you are low on fuel and you drop the bike it can all end up on one side. If that side is opposite the pump then the pump will only pull in air until the bike is upright. Dunno about GSA's but my GS had no sort of connection from right to left or dual pipes to prevent this

 

[jeff]

Have already posted on this (2010 gsa wont start)

Same problem. Bike went over on right side. I would say tank about 1/4 full. When righted would not start. Mechanic diagnosed FPC. Because of the mass of posts on FPC I think we become brain washed into thinking any fuel problem lies at its door. Recovered by BMW to maindealer in Hasnia Crete.

Before bike left on trailer we stuck five litres fuel in it to make sure there was enough to get it back to where we live and cover mechanic test driving it etc. As we had tried for three days to start it flattened and recharged battery three times it never occured to us to give it on last try.

Later that evening got a phone call from BMW assist (who incidentally were excellent - thanks John and Maria - that dealer could find nothing wrong with bike.

Next day into Hania and meet mechanic (technician) Great Guy. Good English Very knowledgeable. Only explanation is that fuel had drained into right side of tank and when bike was righted left side of tank was dry.

He showed me new pump and explained where it picks up fuel. There is he said a device that pulls fuel from right to left side on GSA but his english was not good enough to explain all the details of how it works but it seems to be partially by vacuum -so may only work when engine is running.

Half way up France with no problems with fuel. Did however suddenly have flashing warning that front tyre was deflating rapidly. Pulled over pretty sharpish as on high Alpine pass with huge unguarded drops. Checked front tyre, no visible problems. Checked pressure with tyre pressure gage - perfect.

Restarted engine, computer decides tyre is now correctly inflated. (cause it is!) Heigh Ho

 

[GrinningGSer]

Thoughts... I believe that the vacuum pump sucks fuel from BOTH sides of the tank with two fuel lines and in normal riding, the levels of fuel in either side of the tank will will be near as damn it equal.

So if you have a fall, with LOW fuel levels, then one side, either right or left, will be full of air. The vacuum pump will always prefer to suck air rather than fuel, so the result is no fuel to the injectors.

The fix is to splosh the fuel around a bit

Any logic in that ?

 

[GrinningGSer]

Today my 1200GSA wouldn't start despite lots of starter motor spinning and I was nearly defeated... then I remembered that 3 days ago it had been on its right side, for pickup your bike demonstrations. The bike was mot started after the demonstration. Solution: lay it down on left side and hear lots of fuel crossing the tank, raise the bike, press the starter and bingo, fired first time.
I therefore re confirm fuel supply issues if the bike is over on its right side.

 

[Fanum]

It's a 'sucking jet pump'

IE, it only works when the engine is running, and it only pumps from the right hand side to the left hand side, where the MAIN (electronic) fuel pump picks up from.

Here it is, part no.1

If there's not enough fuel in the LHS to start it, as suggested above, lay it down to slop some over or add some more fuel...enough to tip over the 'hump' inside the tank so it fill up both sides a bit.

The 1150GSA had a simple link pipe going from the bottom of one lobe to the other side, so gravity fed the sides equally.....In theory, it would be quite easy to put in a link pipe on a 1200, but it would involve drilling into the tank, sealing the holes and adding at least one QD so you could get the tank off without too much aggro.

Parts for doing that are obtainable from people who service commercial dishwashers etc...I used to use them quite a lot for adding some quite nasty chemicals into pressurised hot water tanks.....it ain't rocket science

 

[David Nimrod]

Long live simple fuel systems, i.e. I put petrol into the filler, and it runs out of the taps and into the Carbs... brilliant!

Like all elegant ideas, it's the simplest one

 

[Fanum]

Long live simple fuel systems, i.e. I put petrol into the filler, and it runs out of the taps and into the Carbs... brilliant!

Like all elegant ideas, it's the simplest one

Luddite

 

[David Nimrod]

Luddite

Works for me!