I recently picked up 2 atv's that have been sitting in storage for 6 years. I picked up two new carbs and swapped them out. Changed all gas/fluids. They both fired right up, but one idles rough and the other idles fine, but dies when giving throttle. I only see one adjustment screw, the air/fuel mixture screw. It doesn't seem to do anything, and doesn't stall the engine when screwed all the way in. How are these YFM250 carbs adjusted?