Re: burping on MD7A
My newly acquired boat came with a MD7A that is not pumping water. I plan to try and flush the system using a trick I saw in an old magazine. The article described attaching a bilge pump to the water intake hose and sticking in a bucket. The water output was routed via a hose back to the bucket. This way a cleaning solution of some sort (water and vinegar maybe?) could be continually cycled through. I replaced the water intake ball valve with a safety seacock. So it will should be easy for me to switch off the outside water and redirect water intake from a bucket.
This is, of course, after I check simple things like replacing the impeller. You might try the bilge pump trick to force any air out of your system (assuming this is even an issue).