As a more insightful possibility, I would suggest "enough to defeat the reasons against". This then requires an account of how one can have reasons against doing something. Presuming such an account exists, it then follows that one is sufficiently motivated to do something if and only if one has some combination of more numerous and more weighty reasons in favour of doing it than reasons against doing it.
The problem remaining, of course, is in the presumption at the head of the previous paragraph: namely, how can one unpack an account of "having reasons against doing something" that (a) doesn't squarely beg the question of having enough reasons to do something (i.e., the problem that was under consideration in the first place) and (b) doesn't just define reasons against in terms of reasons for (which would move the argument in a vicious circle).
I tend to think that one has a reason against doing something when either (and these are not meant to be exhaustive) (1) doing it is impossible, (2) doing it is imprudent, (3) doing it is illegal, (4) doing it is immoral, (5) one would prefer not to do it.
So, if one can do it, it is not a bad idea to do it, it is legal and moral (at least permissible, it not required) to do it, and one has the preference to do it -- and all these reasons sum, with weighting, to more than the reasons against -- then one would be motivated to do it.