a really weird ninja-movie

I remember watching this ninja-movie back in the 80's when I was a kid, I think it was one of my cousin's movies. It had one of those really eighties-like drawed covers, of a red ninja riding a speed-motorcycle whilst shooting a submachinegun at another ninja following him on another bike behind him I think (doesn't get anymore eighties than that).
The thing that was reeeally weird about it was the content. Sure, it started out as an ordinary 80's action b-movie, with odd 80's fight-sequences and such, then it got to a point where he met his girlfriend I think, they kissed, and then they kissed some more, then they stripped, and then all of a sudden it wasn't a ninja-movie anymore, it was a bona-fide x-rated porn-flick!!! full frontal nudity and everything... you could even see the old in-out in-out.
After that it got back to the story, 80's action movie b-rated, then some more porn (on a beach, the hero's sidekick and his broad I think) then more action, then more porn and so on and so forth...
Now, the question I wish to pose upon you all, is: Does anyone have any idea what this peculiar movie is even called? As I said, I saw it ages ago, and can't remember anything except the cover and the content.
It was kinda funny, back then my reaction was "wtf?" now my reaction when I think back is "wtf haha".
Anyone know this movie or anything like it?