Low Power GT40

[Rideaneversummer]

Hello, I'm a new boat owner. This spring I bought a 1997 Hydrodyne Nexstar V-Drive with a PCM GT40 engine that has 720 hours. When I bought the boat I took it to my local dealership and had them check it out. Everything including compression checked out good. I've had the boat out several times and it starts every time, runs well, but seams like it doesn't have as much power as it should. Last time out, I filled up 2 350lb fat sacs and we had three very skinny adults and two very small children ~400 lb, for a total of 1,100 lb. I tried to wakeboard and the boat would not get up to speed and plane out. We were able to surf just fine with that much weight in the boat, and after emptying the fatsacs my daughter went tubing and the boat was able to plane out, but it seamed like it took to long to plane out. It's my first boat, but I would think it should do better than that.

Since I don't know the history of the boat or when the last 100 hour service was done I am going to go ahead and change the spark plugs, wires, cap & rotor & fuel filter. Is there anything else I should be thinking about? Do I just need to get a different prop? The original 3 blade should be able to pull 1 wakeboarder with 1,100 lb in the boat I would think. Any suggestions would be appreciated.

[Brichter14]

I would say get a new prop for the first thing. That three blade "should" be able to plane you out but who knows, that could be a very low pitched prop. Whats the boats speed at about 4500 rpm?

[Rideaneversummer]

I would say get a new prop for the first thing. That three blade "should" be able to plane you out but who knows, that could be a very low pitched prop. Whats the boats speed at about 4500 rpm?

I may end up getting a new prop eventually, but that's a lot of money the be throwing at parts. More importantly, I'd like to find out if there is some other problem that needs to be addressed.

The boat runs about 40 MPH at full throttle.

[kend]

change the spark plugs, wires, cap & rotor & fuel filter. Is there anything else I should be thinking about? Do I just need to get a different prop? The original 3 blade should be able to pull 1 wakeboarder with 1,100 lb in the boat I would think. Any suggestions would be appreciated.

I think you are on the right track; there is nothing wrong with a good 3 blade but you might make sure the pitch/diameter is the right size for the boat. I would check fuel pressure to make sure the pump is getting the carb (I assume) enough fuel.

[Rideaneversummer]

I'm going to buy a fuel pressure check tool at Harbor Freight tomorrow.

I also looked at the prop and did some research, and it is a Johnson (OJ) Legend propeller that is 13" diameter with a 13 pitch. I don't know what the implications of that are, but that's what I'm starting with. I guess a call to Wakemakers or Acme propellers would probably give me some more information on the right prop for me.

[kend]

OJ 13x13 was a very common prop, but I thought it was phased out by '97; it seems kind of small for a GT40/21' boat. You might see if you can find out what other people with that boat (if you can find anyone) are running. When you say it does not plane, does it not build the rpm or just not get the speed or both

[Rideaneversummer]

Ken, near where the prop is stamped with "OJohnson" it is also stamped "1 93", which could be a build date for the prop. In the 17 year history of the boat that I know nothing about, it's quite possible that a PO wrecked the prop, and replaced it with one from an older boat that they found used somewhere, who knows?

I was on the wakeboard, but I think it just isn't getting the speed. It doesn't seam to have a problem revving.

There is a guy Wakeworld who has a Nexstar. I'll get ahold of him and see what he is running.

[DanielC]

The GT-40 should run about 5,000 RPM at WOT, normal load in the boat.

[vision]

Too much weight in the back possibly. If you overweight the stern the boat will greatly struggle to achieve speed.