About two months ago I posted this problem:

I have a 2005 90bf four-stroke. It has 500 hours on it and I have had it serviced every year since I have had the engine. It has run perfectly save for one problem: At full throttle (above 5,000 rpm), the engine will run perfectly for an extended period of time (8 minutes and the problem usually occurs) and then the red light and alarm come on and the engine shuts down to idle. The water coming out of the pee spout is cold; the light and alarm go off in 3-4 seconds, and I am up and running at full speed again. If I keep the rpm under 5,000 the engine usually runs all the time (it has cut out only once under 5,000 and that at 4,800). I have had new filter, new casing around the impeller, new thermostat put in, all to no avail. Oil pressure is fine and plenty of oil. They are scratching their head where I have the engine worked on as to what the problem is. I would think if it is an overheating problem, the water coming out of the cooling would not be cold and it would take longer than 3-4 seconds to get back up and running.

NOW THE UPDATE:

I finally had the problem solved when a Honda rep came to the shop where I have the engine worked on and, when told I go to a lake about five times a year that has high alkalinity, the rep said I probably had a lot of calcium buildup. They pulled the head gasket and it was loaded with white powder and calcium. Cleaned it all up and flushed it. Runs perfectly fine now. I talked to a friend of mine who guides on the lake and he says he has to regularly flush his Honda engine with a garden sprayer filled with white vinegar. It does the trick.

Lesson learned here, and advice to all who fish lakes with high alkalinity, use the flush port in the back of the engine just below the cowling and purchase a garden sprayer, hook it up to a hose and fill the sprayer with vinegar and let the water run until the vinegar runs out. Engine does not have to be running. Do it after a couple trips if you go to lakes with high alkalinity. Will save you a lot of headaches and money (my total cost BEFORE pulling the head gasket and the cleaning was over $300). Cost of sprayer and vinegar less than $10.

Hope this helps

Very good information, good to know.
Thank You!

__________________
Regards
Boats.net
Honda Outboard Parts