Short answer is you need to use a different bearing. Small bearings (K, E, etc) are suitable for looping, and large (C) bearings are not.
If you look at the 2a yoyo setting cheat sheet here: Loop Setting Cheat Sheet (2a)
you will see that to adjust a yoyo to loop more upwards you can shorten the string, widen the gap, or use thinner string. However, using a wider gap or thinner string lessens the response - which is already in trouble with a large bearing. So the last thing you can really tune is to use a smaller bearing design, so you can adjust the rest of the yoyo to work acceptably for looping.