I have a bike that has been sitting for a few years without proper prep. I just replaced the tires, battery, and oil, but haven't flushed the fuel yet so it has some pretty old crap in there. That said I started it up and it sounds and runs well - no blockage from what I can tell.
The downside is there is smoke coming out of the exhaust (looks greyish), so I'm worried there is much more wrong than a simple flush would fix. I'd appreciate any advice.. if you're feeling extra generous PM me and I can call you