I'm willing to bet there's a crack in the crankcase, probably not visible to the naked eye but I'm certain there's one somewhere and the carb is another possible issue.

That dumbass in the Porsche should get a slap in the face for not stopping to let you drive off the road. I've been told by a friend of mine about a story that he was once driving his Bruiser (yes, Tamiya Bruiser) around his street and his neighbour which was an old grumpy woman got in her mini van then waited for him to get his Bruiser back on the street by her driveway and then drove right over his truck intentionally. This was like 15 some years ago, and she didn't like kids.