Low Power GT40

When you changed out the spark plugs, did they all look pretty much the same? I agree with Skutsch, even given the different boat configuration a GT-40 should easily push it over onto plane with the weight you are talking about. I wondered if you've got a cylinder that's not firing, it can be surprising how smooth running an engine can be firing on 7, yet obviously limiting power quite a bit.

You say "RPM's are fine", but you haven't got WOT rpm numbers. What are you seeing it spin up to when it's trying to get on plane? Is it bogged down at 3,500 or so?

Andrew, where are you at in WI, I am down in the Racine area

Hmmm, I have a 98 Sport Nautique, also 21 foot with the GT40. I regularly wakeboard with 1400 lbs of ballast and anwhere from 3 to 4 guys all over 200lbs (shhh don't tell the coast guard), I have no problem getting up on plane or when shuttling people back to the beach getting it to 40 mph. I have used both the ACME 422 (12.5x15.5) and 1442 (13.25x15). Without the ballast (because we barefoot too)I see top speeds at 44 to 46 mph depending upon the prop. We also surf with over 1600lbs of ballast.

Now the V-Drive is the big difference between our boats (ok, one of...) but I would think the GT-40 would get that boat up on plane. Something doesn't sound right. I would think with the pitch that low, you would have a hell of hole shot and then would really be over spinning on the top end.

Do you have any WOT un ballasted data?

So any update on performance after your "tune up" After all that their isn't much else to do without digging into the computer, I would think.

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.