Most common reason for running excessively rich on a carb is a fuel level issue in the bowl. Too high of a fuel level in the bowl causes rich condition. Most typical reasons are that the float developed a leak (brass) or became saturated (composite float) or there is a piece of trash stuck in the needle/seat interface. On a new or rebuild carb, I would suspect an incorrect float height setting (accuracy is usually within a 32nd of an inch) or trash in the needle/seat. With new fuel plumbing, it would not be surprising to find junk in the needle/seat area, especially if you didn't flush the lines before connecting to the carb. I flushed two gallons through my fuel system with a filter before first start and got a lot of junk.
As others stated, be sure you are rich. A "bog" is most typically experienced when increasing throttle into a lean condition and is often due to insufficient enrichment from the accelerator pump. If the engine regains performance in a couple of seconds, it is the accel pump. If it continues to labor at noticably low power, it is a lean mixture. Lean conditions are typically not characterized as rough running until just about the point where the engine stops. An overly rich condition produces rough running with reduced power output and classic black colored exhaust and if bad enough cause the engine to roughly quit. Even inexperienced folks don't typically characterize the condition as a "bog."
Assuming this is not a transient accel pump issue, you can try accelerating into the bog condition and then pull slowly back on the red knob. If it eventually gets better, you're rich. If it just gets worse, you're lean. The mixture knob meters fuel out of the bowl and before the jets. Therefore it can compensate for the increase fuel flow due to the high level in the bowl.
RV-6A / IO-320, Flying as of 8/2015
RV-10 in progress
Last edited by lr172 : 05-17-2018 at 01:14 PM.