everburn to AFTERBURNER!

I'm having the same problem with my Encore 2550 cat. Things are great for about an hour, then I get a big temperature spike for about 30 minutes or so. It seems like a new kind of gas is being given off by the wood during this 30 or so minutes because flame appears that was not there before and I get a 100F or so stove top temperature rise. I came across this on burning wood

http://www.holzpellet.com/en_pellets_verbrennungsprozesse

I don't know what most of it means, but down at the bottom is "Stages of the wood burn", and this seems like what is going on.

The thermal decomposition takes place at a temperature of 160 – 180°C (Pyrolyse und Degassing phase). With rising temperature the decomposition increases. 250°C onwards it is on its peak. Now the decomposition generates more warmth than it uses up. In this phase the pyrolyse-reactions are strongly exotherm. The wood has lost about 85% of its mass (water, carbon and combustible gases). Charcoal is left.

Click to expand...

250C is about 500F, so I'm figuring when the wood heats up to 500, it gives off the most gas. When my flames go out, all I am left with is charcoal.

Anyone else think this might be what is happening? If I can cut down on the primary air, will it make it burn slower?