Mercury 650 Thunderbolt 4 cylinder

[kj1956]

I recently bought a 142 Predator Bass boat with a 650 Thunderbolt outboard.It needed cables and hasn't been run since last year.Got the cables on added new fuel and a can can seafoam in a mixture of 50:1,carry it to the lake starts seams to run good open it up and about 5 to 8 mph falls flat on its face added new plugs get same results look at the throttle and it opens carbs wide open.My question is what to check next?

 

[GA_Boater]

Welcome to iboats.

I would put in a new fuel pump diaphragm. As the rubber ages, it stretches and can't provide the volume for higher speed running. If you can reach the bulb or have a buddy, squeeze the bulb when it starts to lay down, If it picks up, the fuel pump for sure.

You should replace the impeller unless you know it's been changed recently.

 

[kj1956]

So far I have put on new cables ,cleaned the carbs twice ,changed the distributer ,and rebuilt the fuel pump and nothing has helped.Open to suggestions.

 

[jimmbo]

Did you synchronize the carbs to the ignition advance?

 

[kj1956]

Started back working on this boat ,worked on the timing some more changed the carbs,now it will plane out but only run about 25 to 28 mph.It want take he gas and go it takes it about i/4 to 1/2 mile to get its speed up.