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Thread: Rpm loss

  1. #1
    dawgdude
    Question for the masses. Mercrusier just gave me a brand new 7.4 mpi longblock to replace a bad one. Took old out, put new in with no other changes. Took it out today and found that I've lost about 400 or so Rpm and mabye 6 mph off the top end. I know it's a new motor but I couldn't resist and I only smacked it for about 15 to 30 seconds. That just seems like a big loss. Think that it's just cause it's a new motor and needs a little time for break in.

  2. #2
    1BIGJIM
    That's alot in my opinion. The first thing I would look at would be ignition timing. Then if you are not happy do a compression check or leak down test. You will not notice much difference after the break in and the rings are seated.

  3. #3
    goneboatin
    I had a bad fuel pump on my 350 Mag MPI and wouldn't let me rev past 4200. I stopped to float a while and when I went to start up again the engine would only get enough fuel to start then crap out. Make sure your pump is good and there's no kinks in your fuel line. It sucks having to be towed in.

  4. #4
    dawgdude
    1BIGJIM, Good call on the timing. For whatever reason the dealership had the timing retarded big time. I started advancing until I had gained back way more than I lost to the tune of 600 rpm and 9 mph!!! I never would have thought it would be that big a gain.
    Anyway, thanks for the response.

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