Poor running 3.0 Mercruiser I/O

[R. Ford]

Poor running 3.0 Mercruiser I/O

My 1986 Mercruiser I/O 3.0, 140 sounds and runs great in neutral but runs terrible when put in gear. It seems like it is starving for gas when it is under load. I have to slowly ease it up to speed, still it will not plane off. Used to run 45mph I'm lucky to get 10mph now. Rebuilt carb, drained old gas, new plugs, wires, distributer, coil, rotor, points. Any suggestions?

 

[bomar76]

Re: Poor running 3.0 Mercruiser I/O

Re: Poor running 3.0 Mercruiser I/O

Weak fuel pump?

 

[TwoBallScrewBall]

Re: Poor running 3.0 Mercruiser I/O

Re: Poor running 3.0 Mercruiser I/O

If there is an interrupt switch, it is hanging up. Same thing happened to my OMC. There is an electronic device that creats an intentional misfire when shifting, supposed to clear once in gear but if the switch sticks or the linkage goes out of alignment then it runs like crap. <br /><br />Look for microstiches on the shift linkage. Check if they operate correctly, disengaged in gear and in neutral, but tripped when shifting.

 

[cobra 3.0]

Re: Poor running 3.0 Mercruiser I/O

Re: Poor running 3.0 Mercruiser I/O

45 mph with a 3.0? What kind of boat and what pitch prop do you use? On my 16 ft open deck boat with a 3.0 OMC Cobra, I can get to 37 mph with a 17" pitch prop....I'm going to try a stainless 19" pitch soon to see if I can get it to reach 40 mph.

 

[TwoBallScrewBall]

Re: Poor running 3.0 Mercruiser I/O

Re: Poor running 3.0 Mercruiser I/O

The 1988 bayliner 19' Capri I have reportedly does 45 with the 3.0. Not sure what prop, and I can't confirm because my engine never got over 3000 rpm before it self destructed.