Mine too,I had 2 fires already,even with the rain cap,homemade arrstor it still sparks like crazy. I think the only solution is going to be to extend the chimney (which I do not want to do),or make up a draft door,and run the shaver on natural draft only.To be honest ive been thinking about doing that anyway,the fan just seems to push the heat right out the chimney,and burn the wood faster.
With my Shaver,my idea is to make a new ash door,one with a draft flap door in it,and install a grainger solenoid on it,and a cover to protect it.I think the draft door needs to be a lot larger than the feed pipe that the fan blows thru,so thats why i am going to build a new door.This should stop the sparks,and improve efficiency due to a slower ,steadier burn,and the oxygen feeding the front of the firebox first,so the fire burns front to back,not back to front like a shaver does with the fan coming in from the rear.