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Will installing a water/fuel separator solve my acceleration/top speed loss issue?

R

rejesterd

Regular Contributor
I purchased a used 2010 G3 V167c with a 50hp Yamaha 4-stroke in the spring. It had around 100 hours on it when I bought it. As far as I know, it was regularly serviced at the dealer where I purchased it from, and it was running very well for the first month I used it (which was June). It accelerated well, planed very quickly and had a top speed of 33-34 mph.

Then about 2-3 weeks ago, I noticed that it didn't accelerate as well, took a little longer to plane, and now has a top speed of about 29-30 mph. It never stalls and I never have trouble starting it or restarting it. The only noticeable things are the lack of acceleration and speed.

I treat the gas I put in with Sea Foam (about 3 oz per 5 gallons), which I stopped doing when I first noticed the problem. I thought the Sea Foam treatment might have been causing a problem, but after reading more, I suspect it's simply water in my fuel. I haven't confirmed that yet, but I will this weekend (by pumping out a small amount of fuel into a clear container to examine it).

So I'm thinking that I should install a water/fuel separator, but I'm wondering if that will actually solve the problem. What do you think? If I was having trouble starting the engine or if it was stalling, I'd certainly take it to a mechanic first. But considering my problem appears to be minor at this point, would installing the separator possibly solve the problem (assuming it's water in the fuel)? Just looking for some opinions on this. Thanks.
 
It certainly would not hurt to install the system in your boat,prevent future problems, Pull plugs and inspect. Is bottom of boat grass free, barnacles free?extra weight on board? Rain water in compartments,full fuel tank? Is engine reaching WOT,top rpms??
 
As Johnny said - A separate fuel water separator can'thurt (I have one on my boat) but doesn't that engine also have a fuel waterseparator under the cowling that holds the small fuel filter? There should be ared ring in the bottom of that housing that will rise up if water has beentrapped in the bottom of that filter. If you're running common ethanol-blendedgasoline sold at 99% of gas stations that fuel can absorb ALOT of water beforephase separation occures. Remember - old red Sta-bil was basically ethanolbecause ethanol bonds with water molecules and can be burned away but evenbonded to ethanol it robs power when being burned. It's when all the ethanol hasbonded with all the water it can hold that you get phase separation and findwater/mess in the bottom of the fuel tank and fuel/water seperator. I've NEVER found water in my seperate fuel/water seperator or the filter under the engine cowling.

Johnny also commented on the bottom - do you leave this boat in the water saltor fresh? Growth on the bottom can really slow a boat down and if it's saltwater, barnacles growing on the borrom and the prop can render a boat unable to reach plane inno time... In a month you'd think you were pulling 5 concrete blocks behind the boat. Check the fuel and filter (although I doubt you'll find signs of waterin the fuel). Check the prop for barnacles/dings/dents. If you're using aportable fuel tank and see no signs of water I'd dump the gas into your automobiletank and burn it there. Refill with fresh gas and preferably 100% gas (noethanol) if you have a station or marina nearby that sells it. You can keeprunning Sea Foam at 2x dose until it's gone and then switch to marine greenSta-bil and add it to the gas ALL THE TIME (not just for storage). The Sea Foamwill clean out a great deal but it does take time and running it at highercleaning dose in my opinion.

Do let us know what you find as the learning never stops for us who like tosteer clear of the Yamaha service mafia.
 
Thanks. It's docked on a clear/rocky freshwater lake, so I don't suspect it's growth on the bottom. I'll be checking the fuel filter for sure. I didn't know about the red ring. It's a permanent on-board tank, and I did increase the Sea Foam dosage the last time I fueled up. I think if I do find any water in the fuel, I'll just siphon it out of the tank with a pump, drain the carbs (if that's easy enough to do), then refill the tank completely with treated gas. If I don't find any water in the fuel, I'm going to check out the prop and replace the spark plugs to see what happens. I'll let you know what I find.
 
I did a more thorough inspection last week, and I'm getting 5600-5800 rpm at full throttle, so that seems good. It doesn't hesitate at all. I also realized I do actually have a water/fuel separator installed (it was just hidden in the bilge behind a black casing). So this weekend I'm going to remove some weight from the boat and check underneath the hull for growth.
 
If you remove some weight, check the hull and prop and find nothing out of the ordinary are you SURE it's not performing the same as it was when you purchased it? Is it still reaching the same RPM as it did at WOT or has that dropped? Where are you getting your MPH speed readings from? A GPS will always give an accurate reading, a speedo that measures via a pick-up tube or one tied into the engine's sending unit that reads teh same way (via water pressure) can start to read slower and slower as growth/sand/silt, etc starts to plug up the pick-up tube or hole. I personally pay no attention to the speedo that is tied into my F115 as that stupid thing and the little port on the leading edge of the lower unit that reads the water pressure seem to always need cleaning to report a somewhat accurate reading... Lousy design = lousy readings.
 
I honestly can't be sure if the RPMs are the same now as they were back in June, but I can definitely tell that it takes longer to plane and the acceleration does feel slower. That's a good point about the reading from the speedometer on the boat, so I'll compare it to my gps. Thanks.
 
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