GZ250 Sluggish, hesitates, slower than normal????

[Todubs]

Hello all! Long time lurker and sponge for all the info presented here! Thank you!
My wife has a 2006 GZ250 and recently found an issues we are trying to deal with.

The bike starts without any issues and runs fine at idle. But, when riding, the bike has no "power." Yes, I know it is a 250cc, but it seems to be MUCH slower than it was last season.

When accelerating, the bike "bogs" and is sluggish, but as the RPM slowly increases, suddenly the engine speeds up quickly and you take off with power. It's like a turbo lag kinda' thing.

Holding the engine at higher RPM doesn't seem to change it, still the sudden increase in power after a slow wait. The bike will go freeway speeds, but it takes a lot of time and is SLOW to get there. Also, the bike seems to backfire more when decelerating/engine braking (little pops from the exhaust).

The bike was parked in our carport over the winter with a full tank and Stabil fuel treatment. Ran fine before winter. This issue happens with full tank and low fuel level. Gas cap looks good. Spark plug was light brown and gapped correctly, even replaced with no change. Air filter and air box are clean and free. Vacuum lines are clear and I can't find any leaks in the carb boots. Petcock flows fine and the petcock filter was clear. No change with or without the air filter in place. No change when tank was flushed and fresh gas added. I drained the carb from the bowl and found no junk.

Any carbs issues with these bikes? I'm thinking I need to yank the carb and hose it out? This issue sound familiar with anyone? Bike needs the post-winter oil change, could that have an effect?

Any help would be great! I have no problem getting dirty and breaking out the tools, but I need an idea where to start!

Thank you for any help!