ARG HELP! I'm thinking of a MOVIE and can't remember its name.....?

Ok theres this old guy and a teenager who hang out. The old guy builds a car out of a delorean or a time machine I don't know. Then they both run from hippies and then drive to a farm and meet darth vader in his dads room. Then he likes his mom but his mom doesn't like him back. So they skateboard to school on a skateboard. Then the Doc old guy says "Great Heavy!" I dont know I think that's how it went I haven't seen it in ten years so its very vague. It starts with a B and ends with Future that's all I remember. Oh, and its not Back to the Future, I know it sounds like that but its not. Oh and the kids name is Marty and the old guys name is Kermet Brown. Anyone know this movie?