XJ 600 Engine problem

Hello! A few months ago, I got the little glow (A begr.) and a 2000 XJ600S. Since one of my car-riding fellow citizens forced me to complete braking in the middle of a curve, I made it long at the end of November. Not much happened, disk off, mirror in the A… , turn signal and a few smaller scratches on the panel. (all on the right) Now to the actual problem: I cleaned it again today to the moth again thoroughly and wanted to clean it afterwards a few minutes So far so well, it ran… but in between I had to realize that the right Zyliner (No. 4) did not get warm (or only hand warm) while the rest heated nicely. Also I noticed afterwards that all the curved (except for the 4th) were hot. So I guess that the cylinder didn’t run. -What can that be? -How can I find the mistake as a beginner? Oh yes: As a student I am always for possible hst cost-effective suggestions to have… 😉 If it has to be, but then rather specialized workshop… I have no idea at all… So may someone feel called to help me… Thanks already in advance!