I am 33 years old and have $80K invested in Fidelity 401K mutual funds. I don't plan to retire until 50. Should I move funds to stocks now?

I would aim for a risk-manged diversified portfolio that generates significant income.  There is the theory that you can be more aggressive when you are young because you have more time to recover, and it makes senses if the market goes up.

But, remember, if you are wrong, you won't know for a decade or more and you'll need to recover with less time. Imagine the market goes down 20 percent in the next decade ( that has happened), now you have 20 percent less money and you're ten years closer to retirement.  Now what do you do?,  Do you get even more aggressive?  

You have to be aware of losing both money and time.   My advice is to start conservative and then get more aggressive as you accumulate gains.    http://seekingalpha.com/article/1260101-the-market-has-recovered-congratulations-youve-lost-28-percent

It would most likey be a good idea so that you can be more aggressive especailly since you are young and time is on your side. Make sure to invest in a number of stocks to spread the risk. My Solo 401k Financial