Surging, Bogging, Cutting In & Out, Got Better

[BTR]

'05 RXT 4-TEC 215HP.

First time in the water after winter storage. Severe surging and bogging at almost all throttle positions. At WOT, revs perfectly smooth to 37 mph, then for a split-second acts like it cut off, then revs again. Keeps repeating this behavior. Speed jumps up and down, up and down, regardless of 1/2, 3/4, or WOT.

Initially never gets above 37 mph, but slowly over the next several minutes begins to go faster and faster. Severe surging and bogging continues for about 10-15 minutes or so, while speeds slowly get faster and faster. Finally, after 15-minutes or so it begins to run normally... no surging, no bogging, 68 mph at WOT.

It never exhibited the roughness / vibration that has accompanied the times it's had a bad spark plug. Given this, and the fact that it resolved over time, what's your best guess as to what caused it?

1. Clogged fuel injector that slowly unclogged?
2. Stuck piston ring that slowly became unstuck?
3. Some other cause?

 

[benjilafouine]

Makes me think of bad timing but if you haven't touched engine, I can't see how this could happen.

 

[Mekanix]

Water in fuel.

 

[Sportster-2001-951C-Stock]

Water in fuel, or fouled spark plug. No doubt it was fogged for storage, this fouls new plugs.. Change plugs AFTER spring startup.

If boat was stored outdoors, rain loves to enter fuel cap if o-ring seal is rotten or gas cap isn't tight.

 

[BTR]

It's water in the fuel. This was the first ride of the season. The tank was 1/2 full with "winter storage" gas. I topped-off the tank with fresh gas right before we got on the lake.

1. Should I add an additive to this tank of gas? If so, what are some good choices for an additive?

2. I should run the tank dry before gassing up again, right?

 

[Sportster-2001-951C-Stock]

Pretty sure you're boat has a water/fuel separator. This device is intended to separate small amounts of water but can be overwhelmed by excessive amounts. It should be disassembled and dried out, perhaps the element should be replaced depending on if the filter is contaminated.

It may not be easy to remove the remaining water if there is any but the tank contents should be "polished" using a "fuel polishing" technique until all traces of water are removed.

Have a google search for "fuel polishing" for details on how this is accomplished.

It's not a good idea to continue running until all traces of water are gone, this can contaminate your fuel injection system. Often where there's water there's a lot of "crud" along with it as well.

Some "dry gas" alcohol can absorb water but I cringe with the thought of putting anything other than the correct amount of fuel stabilizer with fresh fuel in the fuel tank of a boat b/c fuel quality is very important to marine engines especially, this includes expensive engines as well as low cost clunkers.

FWIW, a guy told me just last weekend his boat was running fine till he filled the fuel tank at a local marina and shortly after he left the marina his engine stopped running b/c there was a huge amount of water in his fuel.

 

[BTR]

Excellent advice! Thank you! I will pursue the water/fuel separator, fuel polishing, and crud removal.

 

[nateccnn]

I had almost identical situation this weekend. First run of the season. I had to add 6 gallons to one ski and 3 gallons to the other ski. The one I added 6 gallons to had the eact same symptoms the OP described. After about 40 minutes of run time the symptoms completely went away. Both machines ran great afterwards. Both machines hit top end speed of 68 in slightly choppy water.

Is it possible I passed all the water in the fuel system?

 

[BTR]

I'm not sure what you mean by "passed." What do you mean by "passed all the water in the fuel system?" Thanks.

 

[nateccnn]

Passed...as in, fuel pump pumped it out of the fuel tank, through the injectors, out the exhaust....

 

[Sportster-2001-951C-Stock]

My guess is yes, assuming water was causing issues it going to pass through. Depending on the amount, you could've been dead in the water instead. Need to investigate how it got there and take action to avoid this.

There's likely some small amount of water remaining though, this may grow algae and come back to haunt, depending on the amount remaining, if appreciable.

If you have a fuel/water separator, it should be serviced as a minimum and emptied of any water or replaced, per the design.

Water in your fuel tank is never a good thing!