Dear Forum, For the last 2 months I've been trying to sort out why my LT suddenly started running bad.  It started whilst on a run out when I noticed the engine braking wasn't as it should be, I'd shut the throttle and the engine would tick over around 2000 rpm, but intermittently....
After that cold starting is only achieved by turning the starter whilst holding the throttle fully open - without choke.  Once firing choke to first detente and throttle held slightly open, very lumpy and smokey until some heat is in the engine, then runs fine, but fuel economy poor.  When it is warmed up, occasionally when held at 1300 rpm, the revs suddenly increase to a tad under 5000 rpm !!! - close throttle slightly and revs return to 950....
So far I've replaced plugs twice (black and wet on removal), drained and refueled tank, changed the Air Flow Meter, changed Coils and plug leads, checked K&N filter - no excess oil, oh yes, stripped the Throttle Position Switch and found OK, but fitted a brand new one anyway.  All circuits appear OK, new Fuel Pressure Regulator was fitted last year, vacuum hose replaced.
At my wits end now, taking my life over trying to find the cause, anyone got a nice brick wall to bang my head on - I've used mine to excess 

Check your valve clearances it could be tight inlets.

Rick,  thanks for that, but I re-shimmed the bike 6k ago and it ran like a sewing machine until now, something sudden has happened to it.  Motorworks (UK) suggested it could be the earths for the injectors so that they spew full fuel all of the time, Barrie Robson (BMW York) suggested the Temperature switch - it was replaced last year with a brand new one - doubt it has folded in a year...?

the sensor might be ok ...but the connector may have corroded up again ...worth pulling apart to test clean
you can test the connection to the temp sensor by pulling the connector from the under seat computer and counting from the left to all the holes till pin10 is the sensor pin 13 is the earth to that ecu ...measure with ohms range set to 10,000 ohms ....cold should be about 3000  ...if higher  suspect the temp connector or earth to it at first instance ...else delve deeper

likewise check the connector with engine warm  same deal but the resistance should have changed quite a bit lower

hope that helps

there is a graph for this in the efi troubleshooting thread  if you look it up

cheers

Cleverbee wrote:....  Motorworks (UK) suggested it could be the earths for the injectors so that they spew full fuel all of the time, .....

The injectors are switched to earth by the FICU so I doubt that's the problem. The Jetronic is a very reliable unit so I would be looking elsewhere first off.

It certainly sounds like a fuel injection issue but likely to be corrupt signal from a sensors so...
+1 what charlie said, but if no joy there then do a proper load test on the battery. You'd be surprised. This can play tricks with the FICU.

Probably broken fuel pressure regulator. After sam symptoms I checked everything I can remember. Finally I replaced FPR with spare one from my garage and everything became normal: no black spark plugs, normal consumption, idle as before.
Regards

good point nino  worth remembering

Problem with FPR is position behind all that boxes, filters, etc. I rerouted FPR on this position https://www.k100-forum.com/t8064-fuel-pressure-regulator-rerouted

Good ideas gents, thanks.

Armed with multi-meter and old FPR I shall bury myself in the garage once more.....

What's that saying....? Patience is a virtue, hmm, let me think about that one !!!

Right then, here's one for the number crunchers that understand more of multi-meters than I do....!!

Measured Pin #10 on the EFI plug to ground with multi-meter set at 2M = 1.03k.

Removed r/h side fairing, checked resistance of Temp Sensor plug to EFI  i.e cable = NO RESISTANCE 

Measured resistance on the pin of the Temp Sensor that goes to EFI pin #10 to ground = 1.8k

Measured opposite pin of Temp Sensor to ground = 0.331k

Measurements taken of engine block on cold engine = 17.3 deg C - According to the graph, should be looking at a reading of at least 3k ???

One bonus (sorry Motorworks and Motobins) found alternative sensor using realoem's part listing on Amazon search - http://www.amazon.co.uk/FAE-33090-Sender-coolant-temperature/dp/B00DQEWR9O  for the brilliant price of £13.26 

Not checked/swapped FPR yet, awaiting Forum conclusions.

Before start to dig in direction of FPR, measure pressure inside fuel system. It has to be 2,5 bar, or 36 psi. Over pressure means black spark plugs, higher idle, higher consumption.

:DNew Water Temp Sensor arrived and fitted, now purrs like a pussycat !!!

First time the Injection System has fouled up - it has been a pain to resolve, but thanks to all who have helped, who'd have thought eh, a simple switch....... or a simple rider