An mc21 on stock jetting (128mjs, stock needles, 38 slows and 72/75 power jets) will run leaner than Honda intended by at least 3%, that may or may not be enough to cause problems.
It's been said a million times, any engine modification may require a rejet.

Personally I'm not a big fan of premix on the road, it's a pain in the neck at every fill up, uses a ton more oil, means carrying a bottle of 2t oil around and obviously with a closed throttle there is ZERO oil to anything.
_________________
Please do not PM me technical questions, if you can't find it on the Forum start a thread