Can't tell for certain, but it could be a .40 or .46. A lot of them were put on ARF trainers, and they had a preset carburetor, where you could only make small adjustments to both the high, and low speed needle valves. The two odd looking blue "wheel collar" parts on that engine on the needle valves are the adjustment "limiters". Probably more of a bad idea, then a good idea! They were trying to provide a product that newbie couldn't mess up too bad. The engines themselves on average are fair. There was a batch that had bad carburetors. Evolution addressed the problem, but I don't know if there is any way to differentiate between the carbs. The .46 is one of the approved engines for AMA event Sport Quickie 500 Pylon (event 424), so I have three of them. Mine are definitely of average performance, but I've seen some that ran great. Most of us in the racing community have found that under the rigors of racing, they don't last very long. If it hasn't been abused, and the price is right, it could possibly give a good service. looking at the external corrosion, there is the distinct possibility that there could be internal rust, and the bearings may need to be replaced?