" I was told that the rpm sensor needed degauzing by running a magnet over the front cover in a circular motion. "

Hi Reuben again. I just noticed this comment in your post. You need to move the magnet in a LINEAR motion back and forth across the area where the sensor is VERY QUICKLY and do not stop the motion right at the sensor area but at the end of your liniar motions. If you do not know where the sensor is, you need to continue this quick liniar motion across the front cover while rotating the engine. This means do this liniar quick travel at many diameter angles all around the cover. I hope this explanation is clear. Later. Bob.