I am happy to report that our problems have been solved. We've run fast for 3 days in a row and stuck right on 185. The four things we did:
- I checked the through hull and it was clear.
- I checked the impeller, but it was in pristine conditions so we put it back in. We do have two spares on board now.
- I did a barnacle buster treatment (well, the hammerhead competing product). We opened the strainer, turned off the seacock, ran the motor while filling with the 1 to 1 solution of Hammerhead (3.5 gallons overall), and then waited 3 hours, and then opened the seacock and ran it 10 minutes to flush it out.
- We changed the engine zincs. I suspect this helped because draining both had a little debris, and i suspect the shop did not change one of the two because it was down to 25% and had broken away from the zinc nut.
The engine is doing great now at RPMs just over 3000, which was giving us trouble before. Thanks for all of the advice here. It sure does help knowing there's a great community behind this inexperienced looper.
