The underlying concern that you raise seems to be how you can best engage students to become self-motivated in their own learning processes, especially "the not so good students", with the resources that you have at hand.
Perhaps you might first reframe this as a question back to the students. What will help you (students) become more self-motivated in your own learning processes? After all, what good will you ultimately do in your quest to give away anything that is either not desired, not understood, or not appreciated for its intent? You may also discover that what you believe about the desire of your students to be self-motivated in their own learning processes is a chimera compared to the desire of your students to just get a good grade in your class. As disappointing as the latter finding is, it can serve as a reality check to recalibrate where you might better spend your time to reach those students who sincerely want to do what is needed to learn and yet still be honest with those students who are just passing through your course for whatever reason.
One solution is to provide no solutions to the exercises at any point in time. Instead, give the exams with questions drawn directly from a portion of the exercises. The self-motivation is the commensurate statement "If you do all of these exercises, you will have done at least X% of the upcoming exam questions". Finally, you could address your desire to motivate self-learning by having an open-door policy to students who want to review the answers to their work.
Another solution is to provide all solutions to all exercises at some point. Realize that, in this day of internet and with the interactions that occur among students, the minute that you open this door for even one student or one portion of the class, you have essentially opened the door for all students at that moment and for all students in advance for all future offerings of your course. You can in this case address your desire to motivate self-learning by stating that exams will have a (smaller) Y% of the questions from the exercises and a corresponding Z% of questions that stay within the scope of the course but go beyond the exercises. Essentially, exam questions from the exercises would test how well students know the material (even if that is only rote memorization) while exam questions not from the exercises would be designed to test their mastery of (knowledge of, understanding of, and ability to apply) the material.
Finally, an intermediate solution is to give only a portion of the answers to the exercises. Again, with reference that students will have these next time around, when you decide this option, you may as well give the selected answers directly along with the exercises. Here, you can also balance how you distribute the questions for the exams. One potential advantage of this approach is that you can reserve some questions from the exercises that you do not give answers so that you can use them on exams. You might also simply give some exam questions that are already answered as exercises just to discover how many students will not even commit to studying what they are given to know it let alone studying to learn it.
In summary, each of the above three options has its own balance of resources and outcomes. I think that none of them are inherently wrong or right. I think that your first calibration point to decide which option you will use is first to discover what your students believe about the concepts of self-motivation as applied to learning.