Fuel Capacity Mystery....

[Bendy toy]

Correct of course but an external pipe looping down from one side and up to the other would balance the fuel level without any of the jet pump malarkey.

It would need a fuel tap on each side but would solve the problem in the most simple way.

 

[Mad_Accountant]

Correct of course but an external pipe looping down from one side and up to the other would balance the fuel level without any of the jet pump malarkey.

It would need a fuel tap on each side but would solve the problem in the most simple way.

I had the same happen on my new 1200 GSA. The bike ran out 18 miles after the fuel light came on. It's not a gauge issue it's the scavenger pump thingy not working (sorry I don't know the correct name for it). Vines replaced under warranty and already had another bike queuing for the same part. It's a known fault and your techie should have known that. The annoying thing about this fault is that there is absolutely no way of knowing that you have this fault until you run it into reserve and run out prematurely. So clearly to check for the fault it is necessary to carry some spare litres (only during the test) and run it right down periodically.

Thank you for posting this useful thread

Ride safe

 

[Bendy toy]

The scavenger / sucking jet pump is an ejector device.

It is simply a pipe junction where fast fluid flow along one side causes suction in a branch pipe. There are no moving parts.

Poor flow from the pump will cause poor suction on the branch pipe. A new ejector is simply fixing the symptom but won't make any difference.

The GS will need a new fuel pump, new fuel pump controller or unblocking any filters.
Its a complicated solution for a simple problem.
However a weak fuel pump won't improve by itself so running out of fuel with litres in the tank is likely to be an early warning of fuel pump failure.

 

[Wreford Miles]

The scavenger / sucking jet pump is an ejector device.

It is simply a pipe junction where fast fluid flow along one side causes suction in a branch pipe. There are no moving parts.

Poor flow from the pump will cause poor suction on the branch pipe. A new ejector is simply fixing the symptom but won't make any difference.

The GS will need a new fuel pump, new fuel pump controller or unblocking any filters.
Its a complicated solution for a simple problem.
However a weak fuel pump won't improve by itself so running out of fuel with litres in the tank is likely to be an early warning of fuel pump failure.

Thanks for that, I think I'll put a call into the two BMW dealers that appear to recognise this problem (Vines and DL) and if they still do I will suggest that SBW gives them a call.

I'm also considering running the bike low before it goes back to see if it happens again and I still have a nagging thought that maybe the trigger was the bike using a lot of fuel when the level was low meaning not enough motive fuel returning from the pump to keep things flowing although I would have thought the tolerance was not that tight on what it can pump and what the bike needs - meaning there should always be enough fuel returning to keep the sucking jet pump working

 

[jeff]

So your highly trained mechanic at SBW believes he can rewrite the laws of physics and make liquids flow uphill unaided?

This I gotta see, tell me more!

Probably the same guy who told me that no matter what the instruments or on board computer says my bike would use the last drop of fuel before it would stop. Convinces me to never go there again

 

[trainman]

is there a case then that a thrashed bike, and I mean thrashed for a good long while i.e. the whole tank, can get to the point where most of the fuel is being used by the engine and there is in-sufficient return fuel to pull enough gas from one lobe into the other and at some point the pump pick up is left high and dry

just a thought - happy to be shot down with a reasoned answer!

 

[Bendy toy]

No shooting intended.

If thrashing the bike makes any difference (IMO unlikely), it would have no effect until fuel level drops below the tank's central hump.

 

[Wreford Miles]

No shooting intended.

If thrashing the bike makes any difference (IMO unlikely), it would have no effect until fuel level drops below the tank's central hump.

Which would have been the case with me as I only had 4 litres left...

 

[jeff]

is there a case then that a thrashed bike, and I mean thrashed for a good long while i.e. the whole tank, can get to the point where most of the fuel is being used by the engine and there is in-sufficient return fuel to pull enough gas from one lobe into the other and at some point the pump pick up is left high and dry

just a thought - happy to be shot down with a reasoned answer!

Not trying to shoot anyone but if your scenario was valid;-

1. it would be a common fault to all bikes (albeit I know many never exceed the national speed limit) and would mean the pump from new was incapable of
providing sufficient flow under certain circumstances. This would be a major design fault.

2. My pump worked faultlessly for 2 years much of it at sustained high speeds fully luggaged two up.

3. As I have sad earlier, you would expect the pump to rectify the problem at lower speeds or stationary at tick over. Mine did not

4. Munich trumps Hertford every time. When I explained problem to Herr mechanic he immediately said it needed new pump, well known problem.
It is sometimes too easy to complicate problems especially with computer readouts. (for example my Toyota car lost power and all sorts of flashing warning lights came on.
Technician (therein lies part of the problem) plugged car in and came up with a myriad of bits that were faulty. I told him that it was only firing on three cylinders, a - looked at me as if I was the village idiot. To humour me he took off air cleaner and one of the coil sticks had melted. replaced it (at ridiculous cost) and car was cured.)
The bike has a pump system that keeps the fuel in tank level when fuel level drops below central frame member. If this is not happening then the most likely explanation is that it is not working correctly. Hertfords obsession with replacing fuel strips is an example of this.

 

[trainman]

guess we can all agree tank and gauge design have some issues! a low fuel warning lamp is all you need IMO

my KTM had two lobes and two fuel taps, much better, but you had to remember to fill up through both filler caps, otherwise you had self imposed fuel starvation!

 

[Wreford Miles]

Update - spoke to a nice chap (Keith) at Vines who having discussed with one of their mechanics agreed it would either be the fuel pump or maybe the sucking jet not being connected properly or being interrupted by something.

I had considered taking the bike to them but having spent some time discussing this with Kevin at SBW and sharing the thoughts from you guys we all seemed to be in agreement on what to do next - an investigation to see if they way the sucking jet was connected/working was the cause and if not that how the fuel pump was performing, the later being difficult as its not something the diagnostics will show, from that perspective it's either pumping or not pumping.

The investigation found nothing and the fuel pump was working (of course I rode it there) however the view of their mechanics who had spoken with colleuges in the industry was change the pump - they had one in stock for a customer which was not due to be fitted till next week so they fitted that one and all under warrenty.

Job well done, although I will carry some spare fuel when the tank next gets low just in case and I will see if I can get it to do it again by pushing on a bit to see if there is anything in the basic design and ability of the pump to supply fuel and keep the sucking jet going when fuel levels are low.

The other positive is they did not wash my ACF50 off, the downside the leant me and 800GS - what a cracking bike for being a hooligan it made the 1200 seemed very lardy when I first got back on but as they do after a few miles you back to thinking there ain't nowt like a big GS.

Happy Ending

 

[fringe]

Update - spoke to a nice chap (Keith) at Vines who having discussed with one of their mechanics agreed it would either be the fuel pump or maybe the sucking jet not being connected properly or being interrupted by something.

I had considered taking the bike to them but having spent some time discussing this with Kevin at SBW and sharing the thoughts from you guys we all seemed to be in agreement on what to do next - an investigation to see if they way the sucking jet was connected/working was the cause and if not that how the fuel pump was performing, the later being difficult as its not something the diagnostics will show, from that perspective it's either pumping or not pumping.

The investigation found nothing and the fuel pump was working (of course I rode it there) however the view of their mechanics who had spoken with colleuges in the industry was change the pump - they had one in stock for a customer which was not due to be fitted till next week so they fitted that one and all under warrenty.

Job well done, although I will carry some spare fuel when the tank next gets low just in case and I will see if I can get it to do it again by pushing on a bit to see if there is anything in the basic design and ability of the pump to supply fuel and keep the sucking jet going when fuel levels are low.

The other positive is they did not wash my ACF50 off, the downside the leant me and 800GS - what a cracking bike for being a hooligan it made the 1200 seemed very lardy when I first got back on but as they do after a few miles you back to thinking there ain't nowt like a big GS.

Happy Ending

Always good to get a happy ending....

The other cause can be exactly as described, the re-routing of the pipework between the two lobes of the tank, believe this has solved the problem for others as well.