At full throttle, a slow go

[Reel Sharp]

Hey guys,
I had my boat out for the first time yesterday and it was a Great Grady of a time!! I have been working on it on and off for the last 8 months now(mostly off). Well after all the great studies on the threads and questions answered here out it went and came back!! Just sticking within a mile from shore "just in case". The only real concern I had was the throttle. I has replaced the gear cables last fall because it would not engage into reverse, so I replace both at one time, problem was fixed. When I went o give it some gas to really test it, at times it would not respond with only a weak response. I trolled for an hour and had it stall out on me a couple times at low rpm. O then took it inshore to do some low speed cruising and sight seeing. After a while I decided to go faster but it pretty much stayed at the speed even when throttle was all the way down. Every once in a while it revved/chugged like it wanted to go faster but stayed slow.
I just went through some threads and one said a ball valve at the tank. Any other thoughts? I replaced the fuel filter as well. Thanks, Norm

 

[BobP]

Hook up a small portable tank with it's own fuel line and fresh fuel if in doubt about boat fuel system.

Are you sure all 6 cylinders are firing, and not three? Check spark.

Half the powerpack may be dead. Happened to me on my johnee 200s.

Check the wiring back there, OMC didn't use tin plated wiring, so open the ground leads etc, and follow them, I had found rubbery wiring, with no copper inside jacket !

 

[Reel Sharp]

I did replace the plugs recently and they are still clean. The engine had about 50 hrs on a rebuild before I got it. I will see if I can look for any other trouble signs from what was mentioned above.