I have found that its a cyclic thing; if I don't work on my car/s and do other things I will eventually come around to a point where I miss it and then get back to it. I also find that if I work on them when I am not motivated, its more frustration than anything else, nothing goes well and there is a high probability that I am going to mess something up and make things worse in the end. While I would love to have it done, I want it done to my standard without regrets.
I have found that all things have their time/place and if I don't force it, it will come and usually works out. I have to remind myself that its a hobby and is supposed to be enjoyable. Unfortunately (or fortunately depending on the point of view) I inherited a very robust interest in many things from my mother; at any given time she would have 3, 4 or 5 hobbies ongoing simultaneously (sewing, refinishing furniture, painting pictures, needle point, etc). For me, I have several car projects going on, several firearms projects, at least one knife building project, playing with my mill/lathe, at least one household construction project, probably a business deal or two being developed, etc.
I will get back to it eventually, the temps have dropped here and despite growing up in ND, I hate the cold. I do have a space heater in the shop, I just have to get off my butt and start it up. I am currently researching putting a 5.7 into my 68 Cuda, so that is my excuse at the moment...