1964 StarCraft jupiter

[Josh691974]

Got a 64 Jupiter that came with a 35 hp us marine outboard. Could only get it to go around 2 mph. Started and ran fine. Gave up on that motor and put a 1984 Johnson 50hp on it. When I got to the lake, it started and ran with no hiccups. The butterfly's were all the way open. Only would get to 2 mph. I'm at a loss. Only thing I can think of is under the floor it's full of concrete??? Both motors started fine and ran fine, no sputtering. But neither of them would get up rpms over maybe 1500? Any suggestions would be greatly appreciated!

 

[F_R]

You are kidding about the concrete, weren't you? But could be full of water.

 

[Josh691974]

That's only thing I can think of. Boat should only weigh 540 plus motor and 2 people. What all I read is a 50hp should push 2000lbs well.

 

[racerone]

Motors are running on just one cylinder.-----Post video of the Johnson 50 trying to push the boat.

 

[Josh691974]

Both were sparking as the in line lights were flashing when put on. Been trying to find video, I'll keep looking or get another soon.

 

[racerone]

Post compression test numbers.----Maybe a plugged carburetor.------Maybe a ruptured diaphragm in the fuel pump.-----Sheared flywheel key.-----Should be easy to determine what the issue is.

 

[Josh691974]

I'm getting ready to go work on the 50 horsepower Johnson now. I'll try to get some videos

 

[Josh691974]

The high jets on bottom were plugged. Goes 28 mph now