Before you start changing a bunch of things, I would wait and fly it for a while. My experience with several Chinese made engines, although not the Tower .75, is that they need a fairly long run in before their mid range comes around and they start shutting down. I normally find that it takes 15-20 tanks of fuel for the engine to really run well. The top end will run well, but the mid and low end will be chancy depending on how tight the engine was.

I have seen people get totally frustated trying to get a perfect adjustment after a break-in consisting of 2 or 3 tanks. As I mentioned, I don't have a Tower .75, but I do have many .46-.52 size engines, as well as 3 .91s, all Chinese, and they have all gotten around to running well. My Tower .46 was like that, as other engines that size. The .91s, which are on the same size case as the .75, all took a gallon or more of fuel to fully break-in.