I assume the difference in the carbs is the jet size. The Walbro number corresponds to the size of the jet. Different carbs would be used in the same saw at different altitudes. So, the WJ 76 comes with the .076 thou jet orifice. Seems like the option for sea level. You guys realize that you can get a set of hole gauges to check the diameter of the holes right? The fuel flow is adjustable regardless of the jet orifice size as well. You can drill out the jet orifice using the proper size bit and your fingers to turn it. After drilling out the hole, make sure there is a chamfer on the input side of the jet. Again, a bigger bit and just spin it with your fingers... Only takes a minute. Ithe hard part will be finding the .076 bit...