I would start with a fuel filter

o.k. thanks again. i was at the boat yard today. boat looks lonley up on blocks and wrapped up. anyway, there is a syncronizer. the fuel filters i am sure are past their prime. and i will change them. asap. so if there is water in the tank how do i check? or do i pump the tanks dry. or do i add a additive? thanks for the help.!
i noticed the props are 16x17. bronze type, is this correct ? or should i resize? i feel so green asking questions that i have no idea about. any way how do you learn !

Are you inboard? I would think 16P would be a little high for a 13500 LB boat with a 1:1 ratio doing 660 HP (I did some searching and found only 34' gran sports, so I am asuming that's what you have). My $.02 is that you're over-stressing the engines and at WOT you're just drowning the engines. However I am not going to do the math for an inboard so I am just speculating.

Best way to learn is to read these forums, tinker, or both.

~Paulr

Chances are that there's a gear reduction on the back of the trannys. The only way to know if the props are right is to have the engines running well and determine if they top out at around 4500 rpm with those props.
Or you could compare to another, similar boat with the same engines and gear reduction.
Go through the fuel system, make sure everything's fully open and flowing. Change the filters AND fuel water separators if it has both. Pour a few cans of Heet in the tanks, then fill them up.
If it's still doing it, disconnect the synchronizer from the tachs.
Gary

Probably running either 1.5:1 0r 1.91:1 trannys. Could also be running 1.5 v-drives.

A boat like that must have a 2/1 reduction gear box. My ski boat uses a 13/13 prop and a 1/1 straight drive and it goes 46 at 4600 rpm.

o.k. thanks again for the input! so i guess the fuel water seperators is the oil type filter in the engine compartment? fuel filters are in the carb? where the fuel line screws into the carb housing? v drives. engines are in facing backwards.

When you remove the water seperators dump the contents into a clear container and let settle. Later check for water on the bottom of the container. If there is more than a little you have water in the gas tank. Water if it reaches the carbs can result in a lean condition at WOT due to water taking up space in the fuel float bowl of the carbs and not letting fuel into the carb. That is my vote if the boat has been sitting a while.

BT :cool:

will the water ever be expelled from the tanks? if there is water in the flost bowls should i dump these out as well. i bet the boat did sit for a while before we picked it up! and desperatly needs a good run! also running it in this condition to us up the fuel, will this be hard on the engines. or should i get the tanks pumped out?

First find out if there is water by dumping water seperator contents into clear container. If there is only a little remove the carbs and turn upside down, replace seperatars and add "water dry" (isopropyl alchohol) to the gas. Then try again.

BT :cool: