[Blas]

I would check the ovbious things first, visual on the float levels, tightness of the carb bowls, fuel filter(s) clogged. Do you have an automatic choke that's stuck? Any smell of rich fuel mixture? Do you have a fuel pressure gauge installed? Plug wires tight, inside distributor/rotor not fouled with moisture and ozone damage from sitting all winter. Coil connections..Any difference in running/idle with air cleaner top removed? Nothing "LIVING" or "NESTING" in the headers? Like you said earlier, something changes over the winter...Simple and cheap things to look for first...As to the entire tank of gasoline replaced, I'd bet not...Not after one winter...Unless...Did you fill the tank with winter blend fuel when you put it away last year? That could be a problem now that it's warmer out...I like "Sea-Foam" fuel system cleaner. I use it in everything gasoline powered...
Blas