Re: 150hp Mercury run great out of water dies when put in gear when in water
There's 2 ways to go about getting the engine to run right.
1. Take all the anecdotal advice from friends and "mechanics" which usually says to replace the most expensive parts without testing anything, sometimes repeatedly.
2. Get the Manufacturers srvice manual, start at the beginning with systematic diagnostics and repair the problems as they are found.
When I bought my XR4, it had a problem at WOT. I knew it, and I got $500 off on the price for owning the problem. Altogether there were about a dozen things wrong, from dirty fuel tank to many adjustments and wrong parts installed by a "certified mercury mechanic".
For about $200 in parts and a couple of weeks of learning and doing, I had one more problem.
I then had to buy a steeper prop because the engine was strong enough to over-rev with the prop that was on it. Gained about 10 mph in top speed just fixing it. Original Owner had no idea that he owned such a fine machine. I didn't modify the engine, just put it in proper tune.
Systematic diagnosis is the fastest and least expensive path to complete repair.
That's usually true even if you have to buy tools to get the job done. Bonus is you then own the tools for next time, or to help others.