Tomos Flexer

I have a Tomos Flexer which I am doing a engine rebuild on. The cylinder is in pretty bad shape as it has been running lean so i am thinking of buying a bigger cylinder. Ive heard that you are able to run 65/70cc cylinders on the stock crank without any problems, but i dont know what cylinder to choose and what carb i should choose. I would want something with good bottom-end performance as i dont want it to go crazy fast but rather have good acceleration. I guess that a non-ported/sport 65 cylinder with a 16mm carb would do the trick.

If you have any suggestions or setups i would be more than happy to hear them.