GT40 has no power

A month ago my '97 Nautique started acting hesitant towards the end of a full day of boating. It was very weak out of the hole and would only reach 3500 rpms (should be 4800). As I continuted using the boat the max rpms dropped to 2500. A friend suggested changing the fuel filter. I replaced the filter which was the original from 1997 (I bought the boat in 2003). Put the boat in the water to test it and it ran great, rpms were actually over 5000. I went to use it this weekend and it was back to the same hesitant, no power, and maximum of 3000 rpms. Can anyone offer me any advise for the next area too troubleshoot?

Thanks

How long did you run it when you tested? The fuel filter I assume your talking about is the fuel/water seperator (looks like an oil filter)? Sounds like you may have gotten water in your fuel. Take the fuel/water seperator off and empty it, look at what your pouring out and see if it's mostly water (clear). Put it back on and run it again. If it runs fine for a while then starts losing power again, you most likely need to siphon and refill. Before you siphon, let some others chime in. If you do siphon, don't buy a new fuel/water seperator, just empty the one you just bought.

Sometimes this could be a firing issue, but it doesn't sound like it though, due to the fact that it was fixed by replacing the fuel/water seperator.

I'm thinking bad fuel.
If the filter fixed the problem then as you ran the same gas it started again seems like a good place to start.
New fuel and filter.
Then see what happens make sure you get all the fuel out and check for sediment.
I would maybe even pull the tank (depending on how the gas looks that's coming out)so you can get a look inside. Sounds like a pain in the ass but pulling the tank may save filters and head aches.

Does anyone know if a '97 Ski Nautique would have a plug for like an OBD code reader so that I could check that?

I am having a hard time believing it is bad gas. The fuel is less than two months old and I have yet to get any water in the seperator bowl or see any other signs of water. I have experience water in my gas with another boat so I am familiar with how it acts and this does not resemble that. I will pull samples again and check though.

At full throttle it runs smooth not sluggish, just no top end. By that I mean the boat only runs 3000 rpms/30 mph, instead of 5000 rpms/50 mph. However, it is very sluggish out of the hole and does occasionally back fire on its way to full speed.

I think you should check the entire fuel system, debris somewhere is restricting the fuel flow thus taking some power. Did you check the fuel pump, those are electric aren´t they? maybe this are the sympthoms before going dead..just my .02

I think I would be setting up a fuel pressure gauge and checking if the fuel pressure drops before I go anywhere else. These can be purchased at any auto parts store and are not that expensive. also take a look at your knock sensor wire and the conditioner unit behind the ecu bracket. check that all grounds are clean as well as the battery connections.

Here is a picture of what I found under the cap.

Maintenance,Maintenance,Maintenance,guys. Check your plugs,wires,ignition components ,etc.,every year or at least every other year.These things can't run on gas and oil alone.This is a great place to find answers,but remember to give as much info as possible.

8122pbrainard wrote:     Marty's correct! Yes, I just had to do the tune up involving plugs, cap, rotor, point set and capacitor on my 312. They only lasted 29 years and I'm really disappointed.

I'll bet the new ones won't last as long Pete. I have heard the replacements quality is not as good.Since hardley anyone uses points anymore, how are they going to make a profit if Pete only buys them once every 29 years I have heard complaints in the vintage motorcycle community.

8122pbrainard wrote: Gary, I've heard the same thing. The actual material isn't as good. I still have the box so I'll check to see if it states: "made in China"!!!

You said a mouthful there Pete! Applies to nearly any product manufactured there.

I just checked the box for the tune up kit. States made in Mexico! Well, not as bad as China! But still half way there!!

Hi their.
I would not bother with the code reader. Their are only a few sensors that will spit out a code.
First make sure your fuel pressure is correct and holding. If the motor is going into power reduction or limp mode more than likley the oil pressure switch has failed (very Common) then their is a possibility of the water temp switch that is in the same circut failing. check timing make sure that the timing is correct, you will have to pull the little grey spout out of the ignition to stabilize timing also make sure when the motor is reved up that their is at least 30 degrees of advance.
At PCM school we were taught to run diagnostics with multi meter.

97Supersport...

Something extremely easy to check would be resistance of your coil wire to the distributor. My parents boat had very similar issues, would run fine but after it had ran a good while, it would start losing power. We checked that coil wire with a multi-meter and found that it was bad internally. As you would barely move/flex the wire, the Ohms would skyrocket. I'm guessing that as this wire heated up throughout the day that it's resistance started increasing to the point of where the spark was missing out and the engine was losing power.

Anyways, one new coil wire later, the boat ran perfectly fine, all day. It's really easy to check, just make sure the Ohm's on that wire are near 0.