Motor starts and runs but then abruptly stops

[Jakeryan27]

I’m new here and just hoping for some insight. We just got this 71 9.8hp mercury outboard and some hiccups to start. We can get it running only in reverse gear which we know is a problem and possibly something to do with its neutral detection switch. So we know that’s an issue to start but in the video I attached it shows it running we’ve revved it but then it seems like there’s a timing problem? And then it just stops. My dad and I are stumped and looking for some help View attachment IMG_7836.mov