I apologize in advance for the long story, but I thought it would be prudent to be as detailed as possible.

First off, the problem I'm having was not happening prior to my taking the bike to the shop to have the air filter and spark plugs changed and the carbs cleaned/synched.

I picked up the bike and it seemed to be running fine. I rode the bike from the shop back to my neighborhood and when I turned up a relatively steep hill, the bike started hesitating while in 2nd gear. It basically stuttered uncontrollably and stalled out. I was able to get it started, but only when I held the throttle open. It would start and run rough and stumble at low rpm, then all of a sudden it would rev high since I had the throttle open and settle into a good smooth idle. When I would put it into gear and starting letting the clutch out while simultaneously getting on the gas, it would start stumbling and stall out again. The only way I was able to get it up the hill to my house is to slip the clutch while giving a lot of throttle. It seems that the engine keeps flooding, but I have no idea why.

I had the bike towed back to the shop and they were able to reproduce the problem easily. However, it's been 4 days and they still have no idea what it could be.

Does anyone have any idea or suggestion as to what the problem could be?! Any and all help is greatly appreciated.

Thanks...