Niggling running fault on 11s

[R-man]

I'm stumped and welcome ideas from other boxer riders...

Over the last year (around 11,000 miles) I have experienced intermittent poor running on my single-spark 1100s that feels like its electrical and not fuel-related; but more like a hesitation than a failure-to-fire.
By observation I have found this is independent of road speed, gear, and bike position (braking or not; lean angle; climbing or flat road).

It sometimes begins suddenly as a slight loss of power and goes away with just a wee bit extra throttle angle; but other days it recurs over tens of miles regardless of adjustments I make.

Major and annual service (96,000) just completed including a fresh pair of my usual Iridium plugs - no change.

Have tested/ substituted lots of parts including:
# Ignition coil (single coil, 2 outlets) winding resistances tested
# Replaced HES crank position sensor plate as wiring had decayed (I'm rebuilding one as a spare)
# Running pair of fatter Magnecor HT leads -checked for shorting, damage and high resistance
# Checked power, signal and earth connections at Battery, and at Motronic 'brain'
# Had a BMW technician check fuel distributor pressure
# Leaky fuel pump connections (checked at recent f/filter change)
# Tested operation of side-stand switch with engine running and at startup
# Tested for air leakage around injectors and throttle bodies
- and it wasn't any of them...

What have I missed, guys?

Getting desperate now (going slightly crazy), I'm scraping the barrel and imagining all sorts of less likely things I could check:
# Possible dead-spot on Throttle Position Sensor (TPS)
# Clutch operation switch in clutch hand lever assembly
# Asking BMW technician to look for fault codes.

Advice welcomed - and if you've read this far there's no such thing as a silly question...
R-man

[slparry]

Try disconnecting the lambda?

[The Teutonic Tangerine]

worn throttle bodies? i.e. wobbly butterflies

[oyster]

Blocked fuel lines; worn fuel pump; failing fuel pressure regulator; gummed up injectors. All past problems on this site.
EDIT: and check the Hall sensor wire has not had its insulation burnt somewhere along its length.

[nab 301]

As above, is the lambda connected and if so is it the original?
I had similar problems back in '09 at 75 k miles ( doesn't seem that long ago ...) A new secondhand lambda cured the problems at the time although there's 30 odd k miles on it since and possibly just a hint of the original problems recently.
Is it ok on W O T? ( when lambda is ignored)
Major service presumably included balanced throttle bodies with no major adjustments needed?
Lambda thread here

viewtopic.php?t=11301

[Duggers]

Based on my recent experience it would be worth checking the fuel pump as my bike running rough until it was replaced.

[Neil178]

R-man, that sounds very similar to my single spark 1100S.
A small opening of the throttle gets rid of the stuttering and it picks up sweetly until the bike speed matches the new throttle position when it starts to play up again.
From memory, I think the Lambda is not used on accelerating, just on a steady throttle, so the advice of the guys here is what I had thought to investigate. Lack of time and a sweet running 1200S means that the old girl is somewhat neglected at the moment.
Please post your findings!

[Neil178]

PS. I changed the same bits as you too, except the crank thingy!

[R-man]

Well well, it was after all the head-scratching the Lambda sensor.

Thanks to the many Trixters who offered ideas and experiences; once I'd tested everything else, £30 spent at a 'breaker sorted it.

Immediately the idle (which has been lumpy, swinging mostly upwards and unstable), part-throttle running and power delivery are much smoother, and I'm a happy bunny again.

Still thinking 'Damn, why didn't I think of that eh?' thoiugh -I'd been guilty of thinking 'Sensor -Yes' instead of how can I test that link in the chain?

Cheers! R-man

[Neil178]

Nice one, glad you got it sorted.
I still haven't done mine!