My 2valve K100 1986 stood unused for about 4 weeks. One of the starter switch wires became undone. A very simple matter to fix once I located the problem.

Before it always started first turn with the fast idle halfway open when cold and first turn, no fast idle encouragement after the engine was warm.

After fixing the starter switch wire it took a number of attempts before I could get the engine running. I tried with the fast idle leaver full, half, closed. Closed seemed best, but then the engine would turn over a few times and stop. After about 5 times it would idle but die when I open the throttle. I had to let it idle for some time before I could get the revs up.

With the fast idle leaver fully open the starter would turn the engine but one could hear it was never going to fire.

Having got the engine running I decided to leave it overnight and try again the next day to see if the cold start difficulty persisted. It did. I got it running again and again left it overnight. Same as before.

The next day I went for a 50km ride after letting the engine warm up.

Since then it has been back to normal, fast idle half open for a cold start and it takes first turn.

I'm curious. I made no adjustments to anything. The battery was not disconnected at any stage. Oh yes, the TPS is disconnected, has been for about 7000 km

Battery may have been a bit low from sitting and then charged back up when you ran it.

duck wrote:Battery may have been a bit low from sitting and then charged back up when you ran it.

I did not think of that! The thing is I had the battery charger connected to the battery - so at the time of trying to start the bike I ruled out the possibility of low battery. Thank you - Your comment reminded me that yesterday I wanted to use the battery charger and found it not working!

I think that's it as far as struggling to start. But would it explain why the engine died when twisting the throttle before it was warm? Which btw has also changed - I can now twist the fuel open immediately after starting.

The K100 I had and the current K75 are like that. I have just learned to accept it and ride them more.

"The next day I went for a 50km ride after letting the engine warm up."

I hope that doesn't mean you let the bike idle until earmed up, as that will ruin the battery and engine in the long run. As the cooling water and lub oil pumps are shaft driven the volume pumped around on idle is limited.

It's better to start the bike and drive off, keeping it civilized initially :-)

Brgds, Rene

I had similar issues this winter with the motorbike taking longer and longer to start (I had to really insist on the starter button for several seconds before it started.) something that got gradually worse.

I got a tip on this site to try and "activate" the fuel pump. A quick tap on the starter button to "charge" the fuelpump, wait 1 second and then try to start. This solved it for me.
Worth a try ?

Lately the bike is now back to its "normal self". And it's "normal self" is exactly the same as what you describe above, with the fast idle half way when cold, no half idle when warm etc.

Other possibilities :
Could it be your fuel pump is at the end of its life and drawing a lot of current ?
Or your fuel filter partially plugged ?

Regards,
Einar.