3.0 thundercraft prop

[Crazydave1243]

I have a 85 thundercraft 16 footer with a 3.0 mercruiser I think. Im not sure about the motor or not. Right now I have a 14x19 prop but my speed is only 32 mph with 3 people on board and 12 gallons of fuel. this speed to me seems really slow Im not sure of the wto being the my tach doesnt work. Just rebuilt the carb and done a full tune up. the boat gets on plane with really no problems on that end. I do need to adjust my carb a lil but i fell my speed is way off. Does this seem right to or Am I in the ball park, Also does anyone know how to adjust the mixture screw on the side of the carb it is a rodchester 2 barrel.

 

[steelespike]

Re: 3.0 thundercraft prop

We need your rpm at max speed to tell where your at.Is the speed by gps?
But yes 32 is slow most likely the boat should run in the low 40s.Woth a 16 footer it might over rev with a 19" prop.
Be sure the carb opens all the way.Did you check compression?

 

[Crazydave1243]

Re: 3.0 thundercraft prop

Im hooking up a tach I had just laying around and going to do a compression test as soon as the rain stops here. If I remember right the numbers should be all above 140. Is this right also my carb is opening all the way but for some reason it really stumbles when you take off and spits back though it.

 

[steelespike]

Re: 3.0 thundercraft prop

I would say compression of 140 would be excellent. Being within 10% between cylinders
is important.Stumbling and spitting could be timing or lean condition.