9= 9 cubic inches
0= basic design series(?)
1= horizontal shaft and Vacu-Jet carb
4 = has to do with bearing type/gear reduction. 4 means nothing special, no reduction
9= Mechanical starter(?) I'm not sure what that is, exactly. Maybe a wind up type?
The date code seems a bit wrong as well. The first two digits do mean year, but the second two are month, as in 06 for June. I'm not sure what the 81st month is. It may be "01", which is January. The next two digits are the day, and the last digit is the plant where it was made. I've never seen a list of what plant is which number.
As to the Pulsa-Jet/Vacu-Jet controversy, there were two different Pulsa-Jets. One had the diaphragm on the side, one had it on the bottom. The one with the bottom diaphragm doubled as a tank gasket. Both Pulsa's had two pick up tubes, while the Vacu-jet only had one.