Typically, CO is produced by a burner that is burning too rich (over-fired). A control board won't cause this. If that is indeed the cause, if you look at the burner, you should see some black soot in the burner assembly. You mention an unburnt/improperly burnt fuel smell, which is sometimes described as a "kerosene" odor. This is a common complaint with gas appliances IF you have been doing painting, varnishing or stripping in the area of the dryer. The fumes, even if it seems to have dissipated, will give that kind of an odor after it is burned in a gas burner. You will smell it most strongly in the clothing after drying. The most common culprit is methylene chloride (CH2CI), an ingredient which is found in many finishes and strippers. If you have been painting or refinishing, the cure is to open windows to ventilate the area.