Potential reasons dinghy Yamaha 25 hp 4 stroke could be "weak" ?

With only 80 hours ? Starts instantly, idles smooth, both cylinders firing, recent (3 months ago) fuel filter change, recent addition of non ethanol fuel (estimate tank is probably a mixture of half gas that is 2 years old and half gas that is 1 month old) But even with just me (180 lbs) can't quite get it on plane (it= Avon RIB center console dinghy about 11 feet) Prop blades not perfect but almost so.

Ran fine before the hurricane last week, but now weak. Maybe hurricane action (it was loosely tied to floating dock) stirred up some gunk in tank and clogged newish fuel filter ? I don't like that theory however as it was weak from the get go after the hurricane....seems like if gunk stirred up it would take a few minutes to foul the filter....oh wait, come to think of it I did let it idle for probably ten minutes before I took off.

Does that sound plausable or something else to check ? Is tank gunk/algae an issue with gas tanks or only diesel ?

I have a 25 Yammy on my dink and if the gas gets old it dosent run right. Suggest you drain the old gas, change the filter and put new gas in. I try to put stabil in as often as possible, but sometime forget. Good luck.

Have you checked to see if you have a bunch of water between the sole and hull? At 9#/gal doesn't take a to equal an extra body or two.

Doesn't take long for gas with ethanol, even with Stabil, to go bad. Been there this season with our Honda 15hp OB and our Honda eu2000i generator, and yearly with our 2hp Suzuki 2-stroke. A true PIA when you've done everything right. And a real PIA to clean up/out the mess.

Get the old gas out. Perhaps you'll have to disassemble the fuel pump, fuel filter, and carburetor and clean everything. Perhaps you'll get lucky and simply run the thing with clean gas. The Hondas do not like the remains of old fuel; the Suzuki could care less after it gets new fuel.

The Honda gurus in our marina swear by running the engine dry each use and using Seafoam treatment.

Given that one reason to own a Honda generator is for emergency use, how can one store gas? Pour the stored gas into the car and buy new each month? Yeah, that'll happen.

You may want to clean the carb and change the impeller. It worked for me.

For years I've been listening to talk like the above re 2 strokes as reason to get a 4 stroke. Eight strokes comm'in up?

jleonard said:

I don't have a Honda but I do rotate the lawnmower etc gas at my house. We've had ethanol for many years now and I just made a habit of rotating the gas about every 2 months. That plus I use stabil. Have not had a problem with any engine.

Click to expand...

We purchase ethanol free for our only gas powered Rib's or boats so don't have the issue. Interested in the discussion though in case we ever have to regularly buy with ethanol. We have had to for the Rib when cruising but burned through it always within a week.

My bet is a plugged fuel filter. Years and years ago I had a 2 cycle dirt bike. All of a sudden it wouldn't get to full power. Out of the hole it was great, then a few seconds of accelerating later it would hit a wall.


Drained the tank, flushed out some sediment, replaced the little fuel filter (a joke compared to today's engines) and it ran like a champ.


David

At the very least change the fuel filter. That will give you an answer. If it's ok then you are done , if not then look deeper.
I carry a spare filter under the cowling for that reason. Although the tank is clean, several years ago the filter clogged. I was just lucky I had that spare as we were several miles from the big boat.

Dune,

I had an Achilles center console with a Yamaha 25 4 stroke that constantly leaked rainwater into the fuel tank until I redid the fuel fill and vent. Symptoms were the same. Could that be it?

Rob

Replace the gas, ALWAYS add Stable, if that does not due it and the motor sounds like it is coming up to speed, check your prop to make sure it is not spinning on the resistance hub. Once they break away it's all down hill from there.

The larger Yamaha 4 strokes (40+hp) with carbs are legendary for carb problems. Some of the airways are tiny and get plugged with a whiff of sediment. As they are multi-carb setups going out of balance/synchronization causes all manners of issues too. It might be similar issues with the 25 hp units too - not sure. With mine (F50) I had to be festidious with carb cleaning and balancing. Once I purchased a manometer to do the balancing it became a lot more managable!
Good luck. If you are facing similar problems just going through the carb basics - whilst tedious - will see you done.

Bottom growth??

I've experienced the problem described by Mbevens. My Caribe with double hull is a POS. Any water which enters the boat finds its way to the space between the hulls. Before you tear into the engine its worth an unplug to see if that could be the problem. I now have a transparent 5" inspection port which I watch closely and find Im often bailing water.
Good luck,-David