2 stroke engine power

[The Artist]

Not bike related so in RB

I am on holiday, got a small boat with a 30hp yamaha 2 stroke engine. 2cyl and from early 90's I think.

Basically, last year we used it, it did a reasonable 12-15 knots and about 20 with only 2 people on a calm day.

Now this year, it is a lot slower. We had 7 people in and it wold barely do about 5 knots. With 2 people in it only does around 10.

It has had a new plugs, fresh fuel, it pumps cooling water fine and starting it is easy. After the entire winter spent outside not under cover, it started 3rd pull.

How do I get it back up to power. I have tried cleaning the carb, it was spotless anyway. All controls work fine.

I would like to know the proper way to set ignition timing advance on it. Anyone know anything about outboards that can help?

[Dischord]

Is it pre-mix or does it have an oil pump? any blue smoke? Could just be that it can't cope with carrying 7 people. Or if it's a really tired old engine may just need a top end rebuild on both the cylinders. Why would you want to go messing with the ignition timing if it's just been sat?
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2012 KTM EXC 250

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[The Artist]

pre mix, no blue smoke. Runs on 100:1

I was told that someone may have messed with the bit that connects the ignition advance mechanism to the carb throttle.

The throttle works like this. A control cable with inner and outer pieces so it slides in and out. This cable pushes a lever which moves the ignition advance plate which in turn pushes the butterfly type carb open.

I would just like to re set the position of the carb throttle opening if that makes sense.