I think Snapperfreak has it nailed down pretty good. It has a safety handle, so it's at least a series 1. The Max engine was later on. IIRC, the black painted engines and handles started in 1990. I would say that series 5, mid to late 80s would be the right call.
#5
shacky
Is that 3.5 MX a B&S? Not going to spend $150 on it but I'm tempted to negotiate.
#6
Snapperfreak
Yes, 3.5 max. $150 is a bit steep but if he'll negotiate I'd say it's worth it.