Thanks for the info Steve. You are right - it turns out the recommended gap is between 1/16" and 3/16".
And, whoa mama, are you right about keeping the blade sharp! This is my first and only chipper/shredder so I didn't know how important a sharp chipper blade is. I let it dull down to the point where I had to push 1" limbs into the chipper chute. But, because it happened over such a long period of time, I didn't recognize how bad it was. After sharpening the blade I found that 3" limbs self-feed into the chipper chute. What a difference!