Took the boat out for the first time this year Sunday. Had run the engine in the yard with no problems prior to. Started under way ok, but could not get over 10mph. You could put the boat in neutral and rpm’s came up fine, but under load it did not want to go.
Cut the trip short 15 miles (1 1/2hours to get there) moved once or twice about 1 mile or so each. Headed home and then it started climbing. I got my rpm’s back. All was good the rest of the way home.

Checked Air filter, and it’s brand new with no blockage
Fuel line was wide open
Only thing I can think of is bad fuel. This is the first year I left the tank full and just added stable instead of empty.

Any ideas what could have been wrong?


PS. Got 1 nice Wolf 15lb (fisrt wolf ever) bunch of cod, all 20-22" (to small) and Red fish all day (sea pearch)

CHECK YOUR COTTER PIN ON THE PROP. If you are hitting RPM then the engine is cranking. The prop may be loose somehow

what kind of motor?
could be a fuel pump

what were your rpm's wot?
depending on the motor, alot of the newer four strokes have a govenor (sp?) to throttle down your motor to protect it when the computer senses something is wrong.

Could be a fuel problem, check the filters for water.

My guess is bad fuel, get a portable tank and try running with fresh fuel.

Just a guess but check out one of your carb's? May be gunked up!

I might as well guess to....coil ?

at this rate you might as well buy a brand new motor :cheers:

When the ethanol fuel caused scale to accumulate in my boat's fuel, the first things to go were the fuel/water seperator and the internal fuel filters. My honda 225 has 3 fuel filters in the engine all of which clogged. The result was very similar to what you are talkig about

think of all the gas you will save going only 10 mph, might be a good thing.

What kind of engine is it... outboard or inboard? Carbs or HPDI... Did they change fuel filters in the fall and treat the gas... did they/you run treated gas into the engine when you winterized... Load it up with Startron and change the fuel filters. If it is a HPDI Change the filter in the VST tank...

This is why I leave my tank near empty! the little water that will get in there will come out Thur the water separator, If the gas gets a little bad, I am filling up any way and the mix should be good to go.

Better then having 120 gals of bad gas to throw away!!

Good Luck!!

he must be out on his second trip.
no word for days :)

Had similar thing on my carb'd yamaha 2 years back. Gummed up carbs due to ethanol...

Sorry All, Was on the road for work, and did not get on line.

I'm assuming bad gas. I will change the water seperator. Purchased a new (old) house that needs 10 ton's of work. Spending every extra minute there and have not had the boat out again yet.

And yes, this year I left 85 Gallons of gas in it. I Always drain, but someone at the dealer told me it's no problem to leave them full as long as you put stabilizer in it. Last time I ever do that.

Motor is a Mercury Opti Max (EFI)

Someone also told me to run injector cleaner through it.

If it's an Opti, it could be bad injectors. That trips the speed control, but it also sounds a beep on the alarm...

fuel filter
or the cotter pin

checked, and it was not the prop slipping. Odd part was not under a load and the RPM's would scream. Put it in gear and it just did not go. That made me think, fuel just does not have the octain for the power.

I had this problem for 2 years and it took 4 boatyards to diagnose it. Changed hoses, Racor, cleaned carbs, checked O2 sensors, etc. In my case, the jet valves on both fuel tanks were clogged.