I've been slowly working my way through bringing a K100RT back to life after sitting in a shed for ~7 years (according to the previous owner) and one thing that I noticed is that it started to run really rough after I was able to get new fuel into it. I rode it to the station on basically empty and refilled with 98 Octane (Premium) in the hope it would compensate for the little bit of dead fuel and lack of recent. When I opened the tank it looked like there was a little bit of smoke in the tank (which might have just been evaporated fuel fingers crossed) and once I refuelled and left the engine started to run rough and would only run "smooth" at or above 1500rpm. 

My plan to fix it is to replace the spark plugs (along with a bunch of other stuff it needed, including a rear main seal and new clutch disc among other things) but when I removed the old ones the and had a look at the cylinder head it looked very sooted (I've attached a photo, I think). The plugs where sooted too but they were probably fairly old too. Would this be typical of a recently revived bike? Should I run an fuel additive or something else to try and help it clear the carbon deposit? 

You probably had a bunch of crap loosened up by the fresh fuel and then had it flushed down to the injectors.  A lot of the inmates here have sent their injectors to a pro to have them cleaned and flow tested.  That might be a good idea for you.

You also want to flush out the tank.  Many bikes that have sat unused for extended periods will have a lot of gummy rubber from the fuel pump vibration damper coating the inside of the tank.

Last, a couple tanks of fuel with Techron fuel system cleaner or Seafoam can often perform miracles for cleaning stale fuel varnish from fuel system parts.  As long as the engine runs at mid-range you might want to do that before sending the injectors out for service.

If the bike has been sitting for a long time, the rings may also be stuck.  Marvel Mystery Oil has freed up stuck oil control rings on a bike I owned and helped a lot with an excessive oil consumption problem.

What is the condition of your air filter? It does sound to me that the fuelling is running rich.

It was pretty meh. There was also a small mud wasp nest in there too that I needed to clean out. I've got a replacement filter for when I start getting it all back together.

Embarrassingly I didn't think to connect those 2 things

Where about in brisbane are you ?

Northlakes/Mango Hill area

A lot of distance involved but when I can get a bank loan for the fuel I can take a ride over. I have camping equipment.
Regards Martin.

MartinW wrote:A lot of distance involved but when I can get a bank loan for the fuel I can take a ride over. I have camping equipment.
Regards Martin.

welcome mate

sounds like a good clean out of the fuel system is in order

carbon is just a sign that some one hasn't been  riding like you stole it ....giggles ...

after you clean out the tank ...and replace the fuel hoses ....all of them...  including fuel filter , throttle body blanking stubs , z hose from bell housing to plenum  and  test -replace the spark plug leads ...and test the coils ...expectations of the fuel pump lasting without cleaning the tank are dubious and a primary cause of poor and unreliable running .

remember k100 8 valve d7ea ngk plugs   not dr7ea ....unless you have copper cables from the coils without ngk resistive plug tops ...if replacing leads look for  the silicon with magnacore  wiring ....bosch sell the appropriate cables economically from almost anywhere  ...but the real deal is ram leads ...same suppliers of ram shocks and cheaper than bmw replacements (and better ) ...also check that the ferules are fitted ( no longer supplied with the plugs )


I would go for a few relatively short distance runs  to prove reliability then a longer run to clean out carbon deposits  ...perhaps the local loop  brissy Tenterfield ...casino . Kyogle ,mount Lindsay  brissy  should sort out the carbon build up somewhat ...?


good luck  ............... many posts in here explaining it all