My K1100 RS engine blew up and I’m today done with putting on a “new” engine. 

On the old engine I once or twice had to do a WD40 job on the Sprang Clutch in order to get it to engage. 

How ever I took two short rides today. Both with one stop. Both times the sprang clutch just spinned and didn’t engage. Had to put it in gear and pull the bike backwards and make a drop out on the clutch before I could start. 

Previous owner of the “new” engine says he has NEVER had this issue and suggest it is my starter and not the sprang clutch

Forte engine flush will do the job.

Put a small quantity of something like SeaFoam ( not sure if that is available where you live ) or something similar. Put a couple of hundred miles on it and then change the oil.  From what I've read something like Mob 1 15-50 works well in the K bike and that is what I use.

Another thing to check is the battery connections.  If they are not really tight and you have a good ground, that could cause you starter issues as well.

I Miss My K so sometimes i read the forums.. I realise you just put it all back together. so next time you open her up.. try this..

https://www.k100-forum.com/t4116-sprag-clutch-cleaning-the-sprag-clutch-and-bearing-replacement

Great post. My “new” engine hasn’t shown any problems since the two first test runs. I’ll use you link and fix my old sprang clutch, just for fun.