An update on the latest with my K. At the beginning of the month I went to go out for a ride and the bike wouldn't start, after a couple of attempts at turning her over I started to smell fuel, upon looking further It was pouring out of the exhaust.
Motobricker's of this forum and Vogle's trouble shooting guide told me that my 34 year old Water Temperature Sensor had failed. I ordered a new one, drained the coolant, dropped the radiator and removed the offending item. It was difficult to get at with a socket and long reach socket so I cut through the connector then removed with a standard socket. Others have said it's easy to get at by removing the air box, that's debatable but it did give me to opportunity to check my coolant, which was still immaculately clean so was saved to be returned to the cooling system.
I tested then installed the new sensor, put the bike back together, added the coolant, started her and let her get up to temperature, the fan kicked in and out so I took her out on the road. Out on the road the bike would miss-fire and splutter under wide open throttle demand. I went home, pulled the plugs, cleaned them with brake cleaner, blowtorch a wire brush then re-gapped them to 0.6-0.7mm. It was evident they had been fuel saturated during the failure of the old temperature sensor. I reinstated them and went back out on the road, the misfire under WOT had been eradicated.
That weekend I went out on a 'spirited' run with a few others. It was pretty much WOT blasts trying to avoid the fast moving rain clouds. The bike managed 140+ miles with no issues and upon the final 1 mile stretch from my house under WOT the bike began to miss and splutter again.
I put the bike on the lift and pulled and tested the HT Leads. I couldn't get a reading from 2 of the leads but that may have been down to reach of my multi meter probes. I wasn't able to pull the HT Leads apart and restore them during the build as they are sealed units but I did the best I could to clean them up, looking in the ends of them now and they are quite tatty looking so due a replacement (now there is more budget for that).
I tested both coils, #1/4 read 2.6 on the input but only 10.5 on the output (should be around 12.6)
I ordered a replacement used coil from Motorworks and a new set of RAM Power leads from BSK Speedworks (reasonably priced) tested them and installed them in the moto.
I took the bike out on the road and the missfire has again been erradicated. All is well. Until the next time.
Additionally and unfortunately, again the 4L thermistor in the fuel level sender has failed and I now have a permanently illuminated fuel light again. Frustrating. I have been in communication with Digikey, Mouser, Future Electronics, RS Components and most recently Microchip Technology and no one can provide nor manufacture any 600 Ohms at 25°C, 0.5 watts and negative temperature coefficient type thermistor's that are used in the early pre-float type fuel level senders. What I'm told by all these suppliers is that BMW would have had the thermistor's specifically manufactured for the production of the early K series. Mouser have suggested I go directly to Panasonic, they appear to be the only people left. How lucky do ya feel...