Is masturbation still a sinful act even without lustful thoughts?

I've recently found Jesus, and am a born again Christian. I've stopped watching pornagraphy, and I no longer think lustful thoughts during the act. I just try to keep a clear mind while I'm doing it, and not think about anything, at all. I really want to stop masturbating all together, but I can't as of now, as I still don't have a girlfriend, yet. But is it really still a sin, even if I do not think lustful thoughts!?