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Heading in tor work this morning same as usual. A few minutes into my journey the engine mis-ired, faltered, picked up, cut out for a few moments, picked up again then just died.
Cranking made it pop and fart but not fire up. Eventually I gave up and got recovered home.

With the ignition on the fuel pump would continuously prime, over and over again at decreasing intervals over a few minutes until it stops priming. Whilst this is going on, every once in a while I got a feeble mis-fire from a cylinder - without touching a thing on the bike - until it settled down and just sat there doing nothng. Cranking the engine makes the pump run but the engine wouldn't start when cranked.

Shut the power off for 10 minutes, turn it back on and it the procedure repeated. Priming constantly but less and less often over a couple of minutes then nothing.

After a LOT of testing, checking, pulling stuff about I've concluded that the crank position sensor is dead. I shut off the ignition, gave it 10 mins, turned it on so thet it started it's messing about then un-plugged the hall effect sensor and it all stopped. Repeated several timeswith the sensor plugged in - messing about. Un-plugged - sits there behaving itself.

So, a new sensor is on the way, I'm reasonably certain that it will cure the fault. I bloody hope so anyway otherwise I've spent £160 on a part I didn't need and I'll still not have a working bike

Hello Pete,
Appreciate the symptoms /diagnosis.. Will try and file just in case for future use..
Can anyone say why those Hall effect doohickies are that expensive? Are royalties due to Mr Hall?

Id on't think that the sensors themselves are that expensive, but they are potted into a plastic housing which is riveted onto a mount plate. The housing also has a magnet clipped to it. I bet if you could get those sensors out of the potting they would be a ten quid item.

One thing that bothers me is that the sensors are obviously a pair, one for each cylinder. You would have expected it to drop one cylinder given that it's highly unlikely that two sensors went out together. Makes me wonder if the fault is actually in the potted joint part way down the lead.

I might dissect the wiring to see if there is a break in it anywhere.

It's often the wiring if you believe what you read on the internet... although so far I've never had to replace ....

I've belled out the wiring on the sensor sub-loom, from the pins to where the wires enter the potting. No faults found in there. I don't think the problem is with the main loom because un-plugging the sensor stops the odd behaviour, plus once I pin-pointed the source of the fault I did pull the loom and connectors about a lot without it making any difference.

The replacement sensor is due on Tuesday. If fitting it cures the fault I'll take a die grinder to the old sensors and see if I can identify the encapsulated IC.

nab 301 wrote:It's often the wiring if you believe what you read on the internet... although so far I've never had to replace ....

That's what I've heard too - IIRC the wiring breaks down when hot - sub standard wiring. Was it the Dan Cato (or something like that) fromGreece that were refurbished with better wire?

Just to wrap this up, new (pattern) part arrived today from Motorworks. Fitted this evening and the bike fired right up.

Glad to be back on two wheels.

Great to see a post ending happily and with info that will help others