Sailmaster 8 revving up then revving back down every ~2-3 seconds

I'm working on a 1982 Johnson Sailmaster 8 outboard. After a bit of fiddling, I got it running, but if I throttle up above ~1/4 throttle, the motor starts doing this twitchy little behavior where, every 2-3 seconds, it revs up for a fraction of a second, then drops the RPMs back down almost instantly. I'm running the motor at full choke, and see this behavior at full and half choke. I have to fight (unsuccessfully) to keep it going without any choke.

I'm new to outboard motors and am not familiar with this behavior. I took a video of it and posted it below. If you have any idea what the cause might be, I'd appreciate any advice.

Thanks!
--alex

https://www.youtube.com/watch?v=Pjaq7RrOMwY&feature=youtu.be

Clean and rebuild the carb. A good soak is the best way to clean it.