I had owned and flown a few Super Tigre 75 engines. These are ringed engines. It's necessary to break it in first before you mount and fly it. That's just the nature of ringed engines, not the carb. Run 5-6 tanks through it and see if you achieve a good idle and transition. Don't use the factory glow plug on it. Use lower nitro content and a castor based fuel.

My favorite Super Tigres that run great are the ABC variety, the 45 and the 61. I have on that has been flown 4 seasons and runs better than it did when it was new. The 10X8 prop worked best on the 45, and a 13X6 worked best on the 61. They like more prop than an OS does.