The smell was dead give away, didn't need any further test. I grew up with farm tractors and the odor of diesel and gas are unmistakably different. The exhaust was red hot and lit the insulation on fire. The engine smoked like crazy, had no power, we sailed it back to the dock no motor. Enough gas had gotten into the fuel bowls that it quit completely with 90 seconds of landing it at the dock. We were in a narrow channel, it was extremely lucky we were upwind from our departue dock. The exhaust mixer was 99% clogged, tapped and soaked in ammonia 24 hrs cleaned up fine.
