Advice pls on outboard issue

[webbfunk]

Recently bought a new Mercusy 15hp, USA model. Have used it only 5 times now, has been perfect up until a couple of days ago. When opening it right up and going full speed it sounds like the engine is labouring. It sort of sounds like it is slipping in and out of gear. When I slow down to just over half way it is fine.

Any ideas what it could be?

Am going in to have a chat with the dealer tomorrow to get my sounder fixed anyway, so will bring it in to them then. But just wondering if anyone had an idea why it would be doing this? Only thing I can think of that has been different is this last trip I topped up the fuel tank and ran the mix ( 2 stroke ) slightly weaker. I ran the orignal tank at 35 to 1 as advised by the dealer, then he said run it 50 to 1 after the first tank. I also spent about an hour on the first trip just varying speeds and not staying at one speed long to break the engine in.

[Beejay]

This might sound silly, but sometimes when I take my tinny out I put the choke on to start my yammy 30hp cv and then i take of and forget to turn the choke of and the same thing happens to me, so im just thinking maybe your not turning the choke off after you get going?

Just a thought.....cheers Beejay

[webbfunk]

Nah, not the choke. I thought it could have been that at first too but definitely still does it with the choke off.

[tangles]

Not cavitating is it?

[webbfunk]

Just had to google cavitating to know what you meant........not sure, when teh engine sounds like it is louder / out of gear it does lose a bit of power, so maybe? How does cavitating happen?

[kriso]

sounds like cavitating to me , might need to reset your trim and try again

[ellicat]

With my vast mechanical knowledge.....I'm going to suggest that it sounds like you are going up a hill

On a more serious note -

If it's cavitating it would probably feel more like a slipping clutch in a car and you would still get high revving rather than a labouring noise.

Check your fuel line is not kinked or have a hole/unsecure connection.

Hope you didn't use ethanol blend fuel with the 2 stroke....like I did by mistake one (yes one and only one)time.

EDIT: Just reread your OP and it may well be cavitation....caused by air bubbles around the prop. Either you prop is too close to the surface or something else is causing an airstream in the water that travels near the prop.

[webbfunk]

Thanks fellas. I think it may be something to do with the trim.....I'm still trying to master that.

[chonna]

make sure the breather valve on your fuel tank is open, otherwise the engine will struggle to suck the fuel in.

[matsmad]

The bush on the prop isnt slippin is it? Mine did the same.