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NEED HELP!!! I purchased a boat with a 1975 Johnson 70 hp 3 cyl outboard. runs great in my driveway, but on the lake, it acts as though its starving for fuel or ignition timing to throttle is off, tried manually moving throttle, nothing. all three cylinders are firing, compression is right around 115 on all three, tried sea foam in the fuel tank, to no avail. runs awesome until i shift it into gear, then just acts as though its bogging down. Im a diesel mechanic, so it shoudn't be too hard to fix, but seems lots different than a cat motor...