It's a 23 horse horizontal shaft, about 300 hours. It runs with no load, but pretty much dies just turning on the blades. Spews black smoke, which I know is a fuel thing. But it also started using a quart of oil every 5 or 6 hours. Compression test shows 120 on one side, 150 on the other. Spark plugs were both sooty black, but both sides are firing. Replacing the plugs didn't help. Any ideas?