Hello,
I recently put in a new factory crate motor into my Baja 275, the mag HO. The book it came with does not clearly state how to break in the new engine. I have had the engine installed at my local merc dealer and am now ready to start the break in process. Any direction/advice is greatly appreciated!

I know there is a definite break in procedure that is included with the paperwork for automotive crate engines from GM. Just don't recall what it is right now or if it would apply to marine.

I would call Mercury and find out, cuz if it blow's up and they find something in the ECM scan that they don't like....you may be SOL getting it fixed under warranty .....jmo

First 5 hours I'd say no full throttle starts, vary RPM while cruising, and no more than 75% throttle. Second 5 hours again, no full throttle starts, vary RPM, and short bursts of WOT operation. You don't want to run the pi$$ out of it but you also don't want to baby it. After 10 hours run it however you like. I'd change the oil/filter at 20 hours.

WOT for about 5 miles - if it's gonna break, I'd rather it break now than middle of season.

...just kidding.

good luck!