I have an 051 AV Electronic, and here are the differences I can see (although mine is an older model, but did come with electronic ignition): Your oil fill cap is on the side, where mine is on top, your bucking spikes are a different style, the air filter cover on mine doesn't have the arrows or say stop or choke, and the recoil cover on mine has the old log logo where yours has the newer style one. I know a lot of these differences may just be from different years. I looked in my Stihl service manual, and it says that the 075's and 076's came standard with a manual oiler, but it doesn't say anything about the 051's having one. Mine doesn't. Mine doesn't have a decompression valve either. The manual also says "the 051 and 076 crankcases are identical on machine numbers 9280310 up to 9218309 and from machine number 9422350 onward." It also says the dry weight with a 53cm bar and chain (21") 051AVE 11.2kg, while the 076 is 11.7kg. That would be 24.64 lbs. for the 051 and 25.74lbs. for the 076. So I guess if you had that size bar and drained and cleaned the thing you could maybe get a close estimate. I know for sure it's a 051, 075, or 076, but I looked through the whole manual and at mine and that's all the info I could find for you. If worse comes to worse and you need to know for sure, the 051 has a 52mm bore and is bolted on where the 075/6 have a 58mm bore and have studs holding the cylinder down. I know a lot of info was repeated from what the guys before said, but hopefully you can get a useful tidbit of info from all this...