So, I let dad start up my bike today even though he apparently hates the thing. (YEAH RIGHT DAD!) He notices straight away that its firing on only one cylinder! It was pretty obvious to me as well, very rough engine sound instead of the usual putt-putting V-twin. Now I'm fairly certain that its only happened today, because the engine's idle speed was roughly half the usual, accompanied with BACKFIRING.... Never ever heard my bike backfire til today so I am confident I haven't been riding on one cylinder before. Checked the temperature of the exhausts, sure enough back one was cold, front was hot, so pretty certain the back cylinder decided to take a holiday on me. I haven't really ridden the bike lately, partly due to awaiting my license and being away for a couple of weeks. Even so it HAS been started/stopped many times when being inspected and generally stuffed around with by me/friends, hasn't been revved hard while cold or anything. What could cause this? My guess is the spark plugs need replacing, or are dirty? Any suggestions as to what else I should check? I gave it a small rev, and the back cylinder seemed to want to come to life with a bit of spluttering, but then died again after one or two wobbly ones, didn't exactly want to rev it hard - worried it may damage something if only one cylinder is going (would it? ) Now, the bike is a 2007 model VTR250, only 5000kms, so I don't think anything is seriously wrong with it (or so I hope!), its still under warranty anyhow, but still... the baby is in pain! . Any help would be much appreciated. Regards, The mechanically inept!