I’m in the process of tuning up this motor. Gas was left in the carb and it was gunky. I soaked and cleaned it, blew out the jets. It idles smooth, runs up ok but—if you run it up slowly there is a spot just after the throttle begins to advance, where it bogs down and will even back fire. So does this sound like a carb issue? If so where should I go from here? Thanks.