Have you tried a different prop on it?
If you have anyone around with a different pitched prop that might help you with the bigger load.
I have a 40 horse Tohatsu 3-cylinder on my 1648 Weldbilt Modified V that I am in need of getting rebuilt but have had a hard time finding someone affordable to do it.
Everyone I have talked to about a new 40 horse have all said it would not run as fast as it did when running well.
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