Pro Boss GT-40 Surging at cruising speed

[The Hamster]

Hi, this is my first post here, or on any internet forum for that matter, so please pardon my ignorance. I have learned a ton by browsing these forums, but i have recently run across an issue that i cant seem to figure out on my 1996 Sport Nautique with a Pro Boss GT-40. I have used the search function, but cant find anything that sounds exactly like the problems im having. Any help or suggestions would be greatly appreciated. Here is whats going on:

The boat starts and idles fine every time. I never have an issue pulling a skier or wakeboarder, but if i am at cruising speed (about 3200-3700 RPM) for several minutes, the engine begins to surge real bad. It never shuts off, but it boggs way down and surges from around 1500RPM to around 2500 RPM like its struggling for fuel. When i let off the throttle and just have it in neutral for a few minutes, i can take back off to the above listed cruising speed again, and after a few minutes the same thing will happen.

I have done the following things at an attempt to fix the issue:

replaced the Low Pressure Fuel pump (i thought it was going bad and not adequately filling the FCC)
replaced the fuel filter in the FCC
replaced the fuel line that attaches to the High pressure pump inside the FCC
replaced the fuel relays
made sure all (i think) electrical connections were secure.

If anyone knows what may be causing this, i would love to hear about it. All thoughts and ideas are welcome.

[functionoverfashion]

I wonder if there's an issue with the fuel line between the tank and the engine. After sustained periods of high fuel draw, it could be collapsing internally. Ethanol-blended fuels caused all kinds of problems with fuel systems in "older" boats when we first saw it introduced, but your boat probably still has original fuel lines, and now they'd be 23 years old. It's a thought, and not a terribly difficult or expensive item to replace. And no, this isn't pure speculation, I've seen it happen with other boats in a very similar fashion, where they'd run fine except after sustained periods of high fuel draw.

Another thing you can try if you have an outboard fuel tank (or can borrow one) is to bypass your fuel tank and lines, and just hook up the small tank to where the line comes in from your existing tank (the low pressure pump I believe). Then, drive the boat the same way and see if you can replicate the problem.

[The Hamster]

Ill give that a go, like you said, relatively cheap and easy. Thanks for your response.

[The Hamster]

I was able to remove the anti siphon valve and fuel pick up from the tank. The screen on the fuel pick up was clean. Then i removed the anti siphon valve from the 90 degree fitting, and learned there was another screen in there. This was one had gunk caked all over the screen. Sort of hard to believe it wouldnt impeed fuel flow. I feel fairly confident this was my problem. Im going to lake test tomorrow and i will update.

[Neptune442]

Maybe you've seen this thread, but this guy had luck with something as simple as replacing the inline fuse on the positive cable located near the battery. Sounds like it doesn't have to be completely blown to cause issues. For a buck it might be worth a shot.
http://www.correctcraftfan.com/forum...power-at-speed

[The Hamster]

I saw that post and checked to see if my boat has one, and it doesnt, that i know of. Its not in or around the battery box at least. Thanks for your response.

[Neptune442]

Ok, so you don't have a wire like this coming off your battery?

[The Hamster]

No i sure dont. Should I?

[wtrskrs]

I was able to remove the anti siphon valve and fuel pick up from the tank. The screen on the fuel pick up was clean. Then i removed the anti siphon valve from the 90 degree fitting, and learned there was another screen in there. This was one had gunk caked all over the screen. Sort of hard to believe it wouldnt impeed fuel flow. I feel fairly confident this was my problem. Im going to lake test tomorrow and i will update.

Welcome to the forum. I saw your first post and didn't realize others had replied already. While I'm not a betting man, I would not be surprised if you've fixed your problem with that screen mesh in the 90 degree elbow at the top of the tank. I had the EXACT same symptoms on my '96 Ski Nautique. We first started noticing the problem during the 20 minute cruise (around 3000-3200 rpm) to our slalom course site. But we didn't initially have a problem in the course since we're at high RPMs (3600 rpm) for such a short time. But the going and returning from the course got worse and worse (happening once, then twice during the 20 minutes, then three times, etc.), and then started to happen in the course, which of course meant we now had to do something about it. I tested fuel pressure and saw it dropping. I did all of the tests that it looks like you did (replaced all filters although I didn't replace any pumps). I was just about to take it to West Coast CC (two hours away) and talked to the head mechanic there, telling him everything we had done. He asked that I check the screen in the elbow first (which I knew nothing about). I couldn't get it out myself; my son with smaller fingers got it out and it was plugged (amazing). Cleaned it out, put it back in, and voila, worked like a charm ever since!

You should be back on the water tomorrow having a great time in your Nautique!!

Gordon

[wtrskrs]

Oh, and by the way, this was many years ago; we bought the '96 new and were anal about fuel, etc., so I was shocked that that screen was plugged up. Frankly, it looked a little like fiberglass fibers; I chalked it up to some fiberglass fibers getting into the tank somehow during boat manufacturing. Anyway, that should be it. If it is NOT, ping me; I've dealt with several other very obscure fuel pressure issues (one I found by absolute dumb luck).

[The Hamster]

I took the boat to the lake this morning after cleaning the screen in the anti siphon valve. I had no issues, and the boat ran like a champ. Thanks for all who responded!

[Neptune442]

Nice work...boy that has to feel good!

[bamaboy92]

I was able to remove the anti siphon valve and fuel pick up from the tank. The screen on the fuel pick up was clean. Then i removed the anti siphon valve from the 90 degree fitting, and learned there was another screen in there. This was one had gunk caked all over the screen. Sort of hard to believe it wouldnt impeed fuel flow. I feel fairly confident this was my problem. Im going to lake test tomorrow and i will update.

I am having the same issue on my '99 Ski Nautique GT-40. Do you have any photos of the procedure you performed to remove and clean the anti siphon valve screen? Is it very difficult to access and remove? Thanks for your help.

[The Hamster]

No, i dont have any photos, but its pretty easy to access. Your whole back seat will come out easily, and you should be able to see your gas tank.

[bamaboy92]

I found this photo in the forum. Is the screen in the hose or the brass fitting?
Thanks for your help.