Does he really say Oh boy in the beginning of every leap?

Yes, "Oh, boy." is Sam Beckett's catchphrase, because he says it enough times so that it becomes his catchphrase. One time he says "Oy, vey". Like "Great Scott" and "This is heavy, Doc" from Back to the Future.

I believe he did do it in every episode. I could be wrong but it seems to me he did. I loved a couple where he and Al said it together. Made it funnier. It amazed how many different ways he could say "oh boy". You wouldn't think it would be possible.

I suggest that you dl and watch a season and the answer will come to you ha ah

I really liked this show but didn't get to watch every episode since I didn't have cable when they were on the air originally. Over the years I've caught up on most of them on reruns but I seem to remember him saying it in most of the ones I've seen. There was one when Al jumped instead and Al might have said it first that time.

I would think pretty darn close to every time. I know that when Star Trek: Enterprise came out I swore that if he spoke that line ONE TIME, I'd quit watching the show. If he ever did, I didn't notice, because I got way too into the show to notice.