Many red flags here. First, carb 640260B is the correct carb, but because of the cost you decided to go to AutoScam and purchase an after market carb which was advertised as “THIS WILL WORK”. As you have found out, it does “Work” but not the way it should for your unit. Generator carbs are very tight, because of the narrow operating conditions. I’m guessing the your new carb is not jetted right for a generator. Second, when you say “it jumps to 4000 RPMs“, does the throttle plate just move or is the governor move forcing the throttle open. You state that the throttle is different, again leading me to believe that this carb will not work properly for a generator. Finnally, have you checked the hertz output at 3200-3400 RPMs? I’m willing to bet that it is not close to 50Hz. Being more the +/- 1.5 hertz off will burn out many pieces of equipment. Instead of showing us pictures of carbs on the internet, it would be better to post pictures of your original carb and the ope you purchased. My experience is that you tried to save money and it is now biting you in the butt. It may take buying the correct carb or finding an experienced mechanic who understands what needs to be changed on the aftermarket carb.