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New plugs in mine and it just seemed to lag when blipping the throttle, and, as Feralworks stated, it's a bit iffy when blipping the throttle for downshifts - as if it's going to cut out (which it did once and wouldn't start cos the clutch switch was cream cracked!!! that was fun ). Fitted a Power Commander and it ran worse, but at least that should eliminate the Lambda sensors - PC and associated quick shifter will be up for sale shortly if anyone is interested

OK， so this is my analysis of the problem which now seem to mostly have vanished (although I had some rough running while on reserve, went away after refuelling so fingers crossed).

My bike has been like this for at least 1.5 year, and it got worse in May when it would constantly idle at 8-900 rpm and on top of that cut out now and then. That was fixed by replacing the lower left coil but it didn't resolve the issue with the 1.5 cylinder idling or occasional drop (or rise) in rpm.

Reading about the throttle bodies and the stepper motors / idling devices I saw somewhere that they return to idle in two steps, first they stop at 1.800 RPM after which they go back to 1.200 RPM.

After cycling the ignition they cycle through their range and settles at the 1.200 position (according to forum tales) which is why ignition on-off might fix the problem temporarily. If the problem was due to hot coils malfunctioning then ignition on-off shouldn't do anything but only letting the bike cool down should return it to normal. The problem would also only occur when hot which wasn't the case.

Also the fact it was often hanging at 1.800 RPM and have a non-smooth engine braking could be explained by a stepper motor sticking at the 1.800 position.

But how would a malfunctioning stepper motor explain the drop in rev and the 1.5 cylinder idling?

Logically, if one of the stepper motors stop at the 1.800 rpm position, the other one returning, the ECU would probably cut the fuel and/or cut the current to one or both of the coils on that side's cylinder. The secondary coil apparently (again according to the WWW) is only operating at low rpm's to assist in a smooth idle and cleaner combustion so perhaps this one gets shut down?

So if the ECU cuts fuel and/or a coil on the side with the malfunctioning stepper motor then that could, theoretically, cause rough idling.

Cycling the ignition on off while placing my fingers on the stepper motors it felt as if the left one was vibrating more as well as clicking somewhat when returning back to it's rest position.

So I ordered a used one from the favourite dealer, popped the old one out, the chrome one the tip of the plunge was quite worn and the brass was visible but didn't seem graded in any way.

I fitted the replacement and started up the bike and it seemed to idle just fine.

I'm not sure if this operation requires some kind of TBS or electronic reset of the stepper motors but it runs quite nice indeed as is...

Just swapped the right hand side coil pack (as sitting on the bike) and throttle pick up is a LOT better - I'm hoping that's solved the problem but fingers crossed til I get it out for a run.BUT, I'm a little bit more optimistic as I put the old coil from the 12s onto my BCR and it ran $hite - but it hasn't been started for a while. If the weather is OK tomorrow I'm going to give it a run

dave the german wrote:Just swapped the right hand side coil pack (as sitting on the bike) and throttle pick up is a LOT better - I'm hoping that's solved the problem but fingers crossed til I get it out for a run.BUT, I'm a little bit more optimistic as I put the old coil from the 12s onto my BCR and it ran $hite - but it hasn't been started for a while. If the weather is OK tomorrow I'm going to give it a run

Let us know an update. I should have added I slow rode London today in first gear (up to 30mph) and maxed out the engine temp before running out of fuel so can say I thoroughly tested it through the temp bands...

Fingers crossed you’ve sorted it Victor, must say your perseverance and logical fault finding has made some interesting reading and as these bike get older will probably help other owners to sort any similar problems. Good luck

victorlaszlo wrote:

dave the german wrote:Just swapped the right hand side coil pack (as sitting on the bike) and throttle pick up is a LOT better - I'm hoping that's solved the problem but fingers crossed til I get it out for a run.BUT, I'm a little bit more optimistic as I put the old coil from the 12s onto my BCR and it ran $hite - but it hasn't been started for a while. If the weather is OK tomorrow I'm going to give it a run

Let us know an update. I should have added I slow rode London today in first gear (up to 30mph) and maxed out the engine temp before running out of fuel so can say I thoroughly tested it through the temp bands...

Took it out today and for the first few miles it was superb and I thought it had solved the problem - then it started running rougher than it has ever run. Fuel light was on so filled up with premium unleaded, fired up okay but was terrible to ride - I had to cover the clutch and keep the revs up or it would cut out (which it did a couple of times). Above 3000 revs it would pull as normal. Starting up it would idle OKish. Not sure where to go next

dave the german wrote:

victorlaszlo wrote:

dave the german wrote:Just swapped the right hand side coil pack (as sitting on the bike) and throttle pick up is a LOT better - I'm hoping that's solved the problem but fingers crossed til I get it out for a run.BUT, I'm a little bit more optimistic as I put the old coil from the 12s onto my BCR and it ran $hite - but it hasn't been started for a while. If the weather is OK tomorrow I'm going to give it a run

Let us know an update. I should have added I slow rode London today in first gear (up to 30mph) and maxed out the engine temp before running out of fuel so can say I thoroughly tested it through the temp bands...

Took it out today and for the first few miles it was superb and I thought it had solved the problem - then it started running rougher than it has ever run. Fuel light was on so filled up with premium unleaded, fired up okay but was terrible to ride - I had to cover the clutch and keep the revs up or it would cut out (which it did a couple of times). Above 3000 revs it would pull as normal. Starting up it would idle OKish. Not sure where to go next

See above...

Just turned ignition on/off while listening to the stepper motors - whirrs once when turning on and twice (different pitch) when turning off but they both sound the same

dave the german wrote:Just turned ignition on/off while listening to the stepper motors - whirrs once when turning on and twice (different pitch) when turning off but they both sound the same

There was a difference between mine, mostly felt on the return.

Also read somewhere that if you take out the stepper and turn on the ignition the piston/plunge would fly away and not be possible to reassemble. After I had it out of course. And of course my curiosity couldn't hinder me from turning on the ignition with the stepper motor in my hand. And the plunge didn't fly away, perhaps that also indicates it was faulty?

This has really got me baffled as it was running reasonable - lower stick coils maybe? just going to be a process of elimination, but I can see it being expensive

dave the german wrote:This has really got me baffled as it was running reasonable - lower stick coils maybe? just going to be a process of elimination, but I can see it being expensive

There's an unplug stick coil, see if it runs worse, if it did that coil was fine - procedure you can try when you experience the bad running. Very (un)scientific.

Thinking being that if a coil isn't working, and you disconnect it, it shouldn't have an impact on the idle whereas a working one being disconnected should impact. I think I even took mine for a ride with all each coil as well as both the lower ones disconnected.

victorlaszlo wrote:I slow rode London today in first gear (up to 30mph) and maxed out the engine temp before running out of fuel so can say I thoroughly tested it through the temp bands...

You may be across this ... the fuel provides cooling and lubrication for the submersed fuel pump. I would avoid running low and particularly running out with high temps as it risks fuel pump damage/ failure. Personally I avoid running below about 4l for this reason.

Pleased to see an IA change seems to have solved your problem. Well done & Fingers crossed!

Justcruising wrote:

victorlaszlo wrote:I slow rode London today in first gear (up to 30mph) and maxed out the engine temp before running out of fuel so can say I thoroughly tested it through the temp bands...

You may be across this ... the fuel provides cooling and lubrication for the submersed fuel pump. I would avoid running low and particularly running out with high temps as it risks fuel pump damage/ failure. Personally I avoid running below about 4l for this reason.

Pleased to see an IA change seems to have solved your problem. Well done & Fingers crossed!

I wasn't aware of that but any issues have always seemed to worsen when the fuel light is on. I thought that it might have somehow been related to poorer fuel pressure when little fuel, although that didn't make any sense to me as that's what the pump is for. Poor performance due to overheating on the other had does make sense. Is the fuel pump replaceable on the 12S, there's no fuel filter to replace as far as I'm aware so is it integrated and the pump is supposed to be renewed at some interval..?

So to fix this, you replaced a stepper motor? One or both?
Please recap what the bad stepper motor did to indicate it was faulty.

Cheers

Droptarotter wrote:So to fix this, you replaced a stepper motor? One or both?
Please recap what the bad stepper motor did to indicate it was faulty.

Cheers

Check back a few posts and I detailed it exactly. Let me know if you still have any questions...