Englander/Summers Heat Venting Problem, maybe?

I hope someone can help with somewhat of a problem I have been having. My Summers heat 55-shp22 has been working great for me, but I seem to be having "dirty" burns. I was reading somwehere that the ash should be greyish-white. I do not have any clinkers, but the ash is a dark brown to black color. I am somewhat concered that my venting might be the source of the problem. I have a 4inch vent pipe with a 3in adapter that was installed to a whitfield before I moved into the house. Thankfully everything fit nice when I upgraded to the Summers Heat/Englander. The vent runs vertical for I'd say 5-6 feet then ends with a 90 degree elbow. I was thinking that if I adjust one or all of the buttons of the bottom of my unit, it would help. Currently my stove is set to:
Low fuel feed-5
Low burn air-4
Air on temp-1

I am just not sure which way to go with them, or keep them all the same. Thank you for all your help! I saw a post on here sometime ago that detailed exactly what the settings dictate, but could not find it in my search today. Thanks to anyone who can help me out!

Here's the thread I believe you're looking for....
http://www.hearth.com/econtent/index.php/forums/viewthread/11888/

If this doesn't help check back. I'm sure Mike or Corie can help you figure this one out.

Thanks Peg, I was looking for that post for about 25 minutes before I just posted. Checking that reply out from Mike makes me think I should increase the low burn air to see if I can get more of a combustion air going...what do you think? Should I try it out or just wait for Mike or Corie to come chime in?

I had the same thoughts about mine but when I checked the low air burn was already factory set at 9. Certainly wouldn't hurt to check yours to see what it's currently set on and post it here but I think I'd wait about changing it until you've spoken to Mike unless your freezing, of course.