I've been band saw cutting 1x6 and1x8 air dried pine, most of it rough sawn.
I rip them in half and cross cut into roughly squares.
The bridging problem occurs when you shut down and let it sit. Yesterday I filled the hopper and drove about 6 miles and then shut down for about an hour. To start back up I turned on the vacume blowers and it looked like I was making good gas but I couldn't make enough to do anything other than idle.
When I looked in the hopper it seemed like I had 2/3's of a hopper full, when I poked it all the wood fell down in,with the wood level now at the funnel.
Now when I shut down for any amount of time I plan to check for bridging, at least until I'm more familiar with the fuel.