R100 cutting out

[Tridentested]

Hi, just hauled out my 81 r100cs from its winter sleep. Fuel on and the bike started easily with the clutch pulled in, but as soon as I either let the clutch out when in neutral or with the clutch pulled in tried to select a gear, the bike engine stops dead. Not sure what's going on but suspect the clutch switch .Any ideas please, and if it is the clutch switch, exactly where is that located?

 

[Gelandestrasse]

That your engine runs means that the starter motor works, the ignition sensor works, coils work and you have power to the coils and the coils are connected to earth via the ignition sensor. All good.

There are 3 items in the rest of the circuit that are involved.

1 - The clutch hand lever on the left handlebar has a microswitch
2 - The neutral sensor/switch on the underside of the gearbox
3 - The diode on the back of the fuse/terminal board inside the headlamp.

The other thing in the loop is the starter relay which has the power to the coils going through it which is cut by the kill switch. Also the clutch switch and neutral switch earth the start relay solenoid depending on their status. It all points to the right hand switch area.

If I were a gambling man I'd say a mouse has been in and crapped on your kill switch/start button.

 

[Bubb]

Sounds to me like neutral sensor is NOT saying the bike is in neutral….so once clutch lever released it cuts the engine.
Try new neutral switch

 

[Tridentested]

Hi guys, thanks for your responses, just to clarify that the voltmeter shows about ten volts when the clutch is pulled in but drops to zero when clutch released or I try to select a gear i.e. when the engine cuts out, but the starter motor turns over on the button whether the clutch lever is in or out. Can't see any obvious problems re switches on the bars, so currently suspect the neutral sensor under the gearbox. Will see if I can test it in situ as it appears awkward to get at to remove.

 

[mikeyboy]

Where are you measuring this voltage?
Or is it just on the dash meter?

 

[mikeyboy]

An 81 cs should have a separate loom for the neutral switch and oil pressure wiring.
The connector is behind the l/ h side panel by the battery box.
Disconnect the terminal there and measure the resistance in/out of gear.
There’s only two wires one is neutral switch other is oil pressure switch.
One multi meter cable to earth other to one of the two wires leading down to the gearbox/ engine.

 

[mikeyboy]

There’s me getting all technotardy,
Is the neutral light actually working as it should?

 

[Gelandestrasse]

There’s no way a faulty neutral switch will cause the symptoms as described.

Before you waste several hours trying to replace the switch, just disconnect it at the cable joint (not at the switch, that’s a bugger) and short the connections. That will test if it is the culprit (it isn’t).

The neutral switch only stops you starting the bike. It won’t cause it to cut out when running. I suspect you don’t have a (complete) clutch microswitch fitted.

 

[mikeyboy]

Probably more to this,we are making assumptions this is a standard 81 cs,
For all we know it might be a fucked about with machine with any sorts of mods,
I’m out till more info is forthcoming.

 

[Tridentested]

Where are you measuring this voltage?
Or is it just on the dash meter?

Hi, just the dash meter and this below the norm if 12 plus

 

[Tridentested]

Probably more to this,we are making assumptions this is a standard 81 cs,
For all we know it might be a fucked about with machine with any sorts of mods,
I’m out till more info is forthcoming.

Hi, to the beat if my knowledge the bike is big standard will try the tests suggested tomorrow, thanks everyone