When it starts to act up, partially close the choke. Does the engine speed increase or decrease when you do that? Also if it’s a fuel problem, it will show up on the plugs. Have you pulled one to have a look?
I've been monitoring the plugs... Sometimes they look great, other times rich... The fresh plugs I just put in seem to look okay, however I will pull them , take a pic and share here for some seasoned advice!