Bike looks good! Nice color, nice fades, lightsource all makes sense. I'd keep that one a while myself!
Fire is really difficult. There are so many styles and techniques, all of them have a different look and feel to them. It really comes down to personal choice on what you think looks good, and how long you want to spend painting it.
To me, personally, the fire is a bit "empty". Let me see if I can explain........your background layer is a bit too thin.....not fuzzy or full enough. The colors are good, the blends are nice, but looks a bit too defined.....once again, my personal opinion. I've seen lots of fire done that way over the years.......and it is MUCH better than my first attempts!
Here's a link for a "how-to" I did on Blue and White fire. The colors are all interchangeable....just start with your darkest color on the first (background) layer, and work your way to the lightest color as you add layers. This is only one of the techniques that are out there. It may help you in developing your own style!
http://www.airbrushtechnique.com/for...ad.php?t=12647
Big D