The biggest issue I see here is that you really don't have a reliable way to win the game. Sure, the burn will add up, but someone with a bit of lifegain or able to take care of Guttersnipe will have you on your heels already. Then you fall back on the Chimeras, but there are only 3 of those, which are handled rather easily. Sure, you have 5 counters to protect stuff, but then you're likely sitting there holding up a ton of mana AND counters for protection while the opponent is freely doing other stuff - the minute you counter their Desecration Demon or whatever, they can remove the Chimera.
For a casual setting, I can see this being just fine, but in a more competitive environment, I just see it struggling without some changes.
A few cards to consider:
Keranos, God of Storms - hard to get rid of, and a definite clock by every definition of the word - worst case scenario he's powering you through land clumps.
Stormbreath Dragon - even as a 2x or something like that, it at least gives you a bit of a beater to finish the opponent off. If you need a budget option for the casual table, Hypersonic Dragon can work in a pinch, but it isn't THAT great.
Goblin Rabblemaster - I think this card is just nuts in so many settings. It creates card advantage and can be a REAL threat all on its own.
Purphoros, God of the Forge - I think if you do decide to slide in the Rabblemasters, this would be an excellent choice given the fact you already have Young Pyromancer and Molten Birth in here. Then again, at this point this is a totally different deck we're talking about here.