Danny said:
So the whole spark thing comes down. To sexual tension and emotional attachment then?
I definitely try to stay away from truisms (saying something is always because of something else).
Just from reading different articles, and my own experience, I've felt the spark the most when there was a lot of sexual tension in the air (like something was stopping us from being all over each other, and the moment that obstacle went away, we went crazy), or when I've actually connected well with a girl, while still being sexual, in which case it's a different type of spark.
Some reasons I can think of for not having that spark:
1. You're not in the moment, i.e. you're thinking logically while kissing her about next steps, versus being fully in the moment.
2. You showed all your cards, so the girl knows its in the bag with you, and therefore there's not really any tension left, but she went along with it anyway for some reason (maybe she was just horny)
3. It could also be a sex/kissing technique thing, in which case you just need to figure out how to improve your technique
4. Maybe the girl's you've been with are just odd, and not the types with whom you'd have a lot of sparks flying
It could also be none of those, since I don't know about your experiences, in which case you might have to think through the issue and come up with potential solutions and test out which ones do the job.
The fact that you are kissing girls and having sex makes me feel that you're generating sexual tension, so maybe what you're looking for is how to maintain it? Maybe a more experienced board member would have a better take on the issue, but I hope my comments were useful feedback for you.