BMW K1100LT

[Davehsw]

Help!

Is there anyone out there who knows these bikes inside out? I have a long running problem that needs sorting or it is off to the great scrapyard in the sky for it...

[Snowy]

Help!

Is there anyone out there who knows these bikes inside out? I have a long running problem that needs sorting or it is off to the great scrapyard in the sky for it...

Whats the problem? I know the RS version reasonably well and apart from the fairing they are much the same. :)

[Davehsw]

It rides absolutely perfectly until I hit a bump and then it acts as if it is struggling to get fuel.

Sometimes, if you rev hard it recovers, and sometimes it keeps coughing until it dies. Then I keep trying until it restarts. Then it will be perfect, or still struggling.

It never, ever, does it near a mechanic!

[Snowy]

It rides absolutely perfectly until I hit a bump and then it acts as if it is struggling to get fuel.

Sometimes, if you rev hard it recovers, and sometimes it keeps coughing until it dies. Then I keep trying until it restarts. Then it will be perfect, or still struggling.

It never, ever, does it near a mechanic!

First things to try:

1. Sidestand cutout switch, can get dirty or faulty - many people bypass it anyway. Easy to do. Look for a two pin connector with red/green and brown wire, RH side of seat. To bypass it put a wire link over both pins in the connector.

2. Fuel pump connector that goes from the tank - 4 pin multi connector RH side of seat. Gets a bit iffy sometimes, usually making sure it's seated correctly is enough, but check the condition of the female connector to make sure they fit home OK.

3. Motronic "Brain" that lives under the seat - can look just fine but the pins don't locate fully. They may just need cleaning. Make sure its fitted correctly. Run the engine and then press down on the Motronic to see if there's a change in rev's.

To be honest, there's a load of other things it could be but from the sounds of it, the likely cause is a loose connection, and the above three are all known candidates and I have had all three with the same symptoms.

[Davehsw]

Thanks Snowy,

I have already bypassed the side stand switch to no avail.

The others will be tried tomorrow. I will let you know.

[Mark_Able]

It's got the wrong badge on the tank Dave. Try either a Japanese or British one... ;) ;D

[Jon_W]

Sounds like fuel starvation. First guess is the fuel pump is cutting out. Also check the vacuum connections on the carbs and the inlet rubbers for cracks or splits.

[Snowy]

Sounds like fuel starvation. First guess is the fuel pump is cutting out. Also check the vacuum connections on the carbs and the inlet rubbers for cracks or splits.

Just to be accurate Jon, this bike has fuel injection.

The pump usually either just works or doesn't and its easy to tell when switching on the ignition. The usual cause of an intermittent misfire in this regard is the multipin connector which goes from the fuel pump (which lives inside the tank) to the main wiring loom.

There is a fuel filter inside the tank that runs from the pump which could be blocked, and this may cause fuel starvation but its not usually intermittent. If it's unknown when this was last changed I would fit a new one asap though. Its easy enough to take the feed of the injector rail, spin the engine over (with suitable container for the petrol) to see if both the pump and filter are OK.

The problem could of course be coil related - if the misfire is on two cylinders (1/4 or 2/3) then thats likely and these can go intermittent before total failure. Another suspect would be the HES but that causes issues only when the bike is hot and the bike will not restart until the engine has cooled down.

Has the bike been stood for a long period of time? If it has, its worth running some fuel cleaner through the system while your at it. Also, double check the short you have in place in the sidestand switch connector - it may have come loose.

Generally, also check all the connections with the electrics including earths etc which may be loose. The main chassis earth is under the tank below the headstock. There is also a small earth on the Motronic under the seat which should also be connected.

These bikes are generally bullet proof but have their known weakpoints which most owners get sorted out and then there's no reoccurence.

[Cemorah]

Fuel pump or Relay that feeds it. Fuel pump is in tank I believe, relay in electrical box under the seat.

I live in Cricklade if you neeed help sent you a pm with contact details

[Jon_W]

Sounds like fuel starvation. First guess is the fuel pump is cutting out. Also check the vacuum connections on the carbs and the inlet rubbers for cracks or splits.

Just to be accurate Jon, this bike has fuel injection.

The pump usually either just works or doesn't and its easy to tell when switching on the ignition. The usual cause of an intermittent misfire in this regard is the multipin connector which goes from the fuel pump (which lives inside the tank) to the main wiring loom.

There is a fuel filter inside the tank that runs from the pump which could be blocked, and this may cause fuel starvation but its not usually intermittent. If it's unknown when this was last changed I would fit a new one asap though. Its easy enough to take the feed of the injector rail, spin the engine over (with suitable container for the petrol) to see if both the pump and filter are OK.

The problem could of course be coil related - if the misfire is on two cylinders (1/4 or 2/3) then thats likely and these can go intermittent before total failure. Another suspect would be the HES but that causes issues only when the bike is hot and the bike will not restart until the engine has cooled down.

Has the bike been stood for a long period of time? If it has, its worth running some fuel cleaner through the system while your at it. Also, double check the short you have in place in the sidestand switch connector - it may have come loose.

Generally, also check all the connections with the electrics including earths etc which may be loose. The main chassis earth is under the tank below the headstock. There is also a small earth on the Motronic under the seat which should also be connected.

These bikes are generally bullet proof but have their known weakpoints which most owners get sorted out and then there's no reoccurence.

Hey! Am no expert on Beemers... just trying to help. If it's injection then i'd be thinking about the crank sensor and fuel pressure valve.

[Snowy]

Fuel pump or Relay that feeds it. Fuel pump is in tank I believe, relay in electrical box under the seat.

I live in Cricklade if you neeed help sent you a pm with contact details

To get to the relay's you have to lift the tank :)

[Snowy]

Hey! Am no expert on Beemers... just trying to help. If it's injection then i'd be thinking about the crank sensor and fuel pressure valve.

I wasn't having a pop Jon ;)

[Davehsw]

Thank you Snowy.

The Old Girl runs again (Motronic plug re-seated).

The restoration project can now continue.

And thank you to all other suggestions which have been memorised for next time ;D

[Snowy]

Thank you Snowy.

The Old Girl runs again (Motronic plug re-seated).

The restoration project can now continue.

And thank you to all other suggestions which have been memorised for next time ;D

No worries, I have had mine for 15 years and know the bikes quite well from doing all my own work. I have the full BMW service manual for reference and there's some good bike specific forums if you're interested :)

[Jon_W]

Hey! Am no expert on Beemers... just trying to help. If it's injection then i'd be thinking about the crank sensor and fuel pressure valve.

I wasn't having a pop Jon ;)

No worries!!!!

Glad the beemer is sorted!!!