97 SN, loss of power, top speed, rough idle

Hi everyone, I'm having some issues with my GT40 and need some help figuring this out to avoid the stealership.

Here are my symptoms in the order they began:

1. Intermittent and slight momentary loss of power (rpm) at any speed (felt like bad gas)

This progressed into:

2. Momentary loss of power (RPM) at any speed (see video - http://youtu.be/z9eSgtXrSi4 )
http://youtu.be/z9eSgtXrSi4

3. Intermittent Loss of top speed - This became progressively worse from not being able to go over 35., then 30ish, now high 20's. When at driving it feels like the boat wants to go faster and occasionally surges but the bogs back down.

4. Rough idle - it will idle fine then suddenly sound like the engine is dying or seizing and the rpms will drop...this is the same symptom as when driving just at idle (see video - http://youtu.be/bcirxCtgV1M )
http://youtu.be/bcirxCtgV1M

5. I don't know if this is related or not.... and these two issues have only occurred once each independently.

      1. Both batteries died....I saw the volt meter on dash slowly creep down over 2 minutes or so and the boat died in middle of lake. Switched to battery 2 and same thing. Recharged system and everything was fine. Batteries are charging and at proper voltage.

      2. Boat would not start...there was no power to anything like there was no battery connected. When turning the key the battery gauge would move very slightly (as if hitting the dash). Tried a few times and all the sudden it worked again as if nothing was wrong

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I have tried the following:

1. Checked anti-siphon valve (OK)
2. Changed fuel filter (NEW)
3. Changed little tube inside FCC, had a tiny crack, however I may have caused it removing the FCC/filter (NEW)
4. Checked and cleaned screen at fuel pickup
5. Added Seafoam
6. Checked for water in fuel (OK)
7. Fuel pressure at idle was 34, when RPMS went down (power loss) the pressure would surge to 38-40 then back to 34. It would basically bounce between 32-38 when the engine sounded like it was seizing. It seemed like the seize occurred before the pressure went up, almost as if the pressure was compensating to prevent the engine from dying. If that makes sense. (***I have not tried it under load, will do that Wednesday)
8. I visually inspected and pulled plugs/wires. (OK, from what I can tell, they are 6 month old)
9. I individually pulled the plugs of cylinders 1,2,3 (one at a time) and started the boat...it ran the same? (I don't know what that means and if I did it correctly but I got zapped so I quit :) - I will try this again when someone can give me some good direction on how to test this properly please. This part also seemed very confusing to me that the engine would run the same with plugs removed of a cylinder...But again, I probably did this wrong.

Any advise would be greatly appreciated and sorry for the lengthy post.

Ok. I checked the fuel lines and they are clear from what I can tell. I wire brushed the battery connections and engine ground.

Would the timing or firing order change? I ask because the engine ran fine and this problem hasn't always been there. I did check the trouble shooting thread but didn't find anything that matched my symptoms exactly.

I have not replaced that.

Ok little update. Today I replaced low pressure fuel pump, cap, rotor and spark plugs. The engine ran a little smoother however I still have a loss of power. Most of the time it wouldn't go over 2700rpm (no check engine light). Sometimes I would get it up to almost 3200. I also had some backfiring which went away after changing the plugs....I was also caught in some rain with the engine cover open so that may explain the backfiring?

Battery 1 was way low showing at around 10v with the boat running. While under load going about 20mph I switched to battery 2 (which was fully charged) and had an immediate power surge and the boat went faster, still loss of power but more power than with battery 1.

This leads me to believe my problem is electrical and not fuel related. What can I check that would cause a hesitation and loss of power related to battery or charging system? Any ideas?

Was the dual battery thing a factory installation?

For each battery, when it is connected, you'll have to check what kind of voltage you are getting at the battery with the motor running. It should be close to 13, if you are getting a charge. You'll need a multi meter for this.

I hope that rebuilt distributor was a marine version and not automotive.

It's not a marine version...it's the same.

How did you figure out that it was the distributor? Wht did it look like?

I have a 1989 SN having very similar issues to what you described, but I have not checked inside the distributor.

Thanks for any helo,
JM

Two different distributors in those boats.