post-winterizing problem

[RobH]

Okay, I'm an idiot, but I don't know what's up with my '86 GL1200 Interstate. I stored it for a few months with a full tank of gas and Stabil. A situation came up, and I had to ride the bike without switching out the gas. If I'm at speed and roll on the throttle, it shudders and misses. If I roll off the throttle, it backfires. I've pulled and cleaned the plugs, with no difference. I've since gone through the gas, refilled with premium and SeaFoam. It starts fine, but if I roll on the throttle it still shudders and misses, and backfires when I roll off.

Before taking it into a shop and spending money I don't have, I'm hoping there would be something that I can do that might identify and, ideally, rectify the problem.

Thank you for the help!

Rob