2013 zx10 i have just replaced the original air filter for a k&n .
Can that cause any problems ?
Never been flashed and its de-cat'ed .
Has a gp growler exhaust .
After starting it it seemed to of got hot very quick .
I dont mean up to temp hot .
It will be running a little leaner now creating that little more heat. Is it damaging No probably not! Even with a de-cat and slip on. However me personally i would now be looking at getting a flash and dyno, just because the bike will be so much sweeter to ride, it'll sound better, and give better MPG. How and which way you want to go with flashing and tuning depends on what plans you have for the bike. If you have stopped meddling with the bike just go along somewhere for a Woolich flash and tune, if your going to constantly being changing mods on the bike then consider buying a tune it yourself set up (more expensive initially)
You don't have to do anything, im sure it will fine. But i would thats just my personal opinion. I don't know where in the UK you are but a full flash and dyno is typically around 400 yes its a lot on money but if your not going to meddle with the bike its the best option and will no doubt pay you back with the grin factor.