Yamaha 250 AET 2 Stroke – How to adjust the Carbs?

[twa2010]

Hello together,
I bought a used 250 hp (Serial: 61A X 1000728).
Unfortunate my boat workshop messed up this engine.
First trying it – I had lots of power – but during idle the engine always stopped (partially with backfire).
Then the mechanics mess the carbs in order to find a better adjustments – with no success. I gave up with this workshop and try to find a solution myself. I realized that two sparks are washed so I replaced all six sparks. I saw also that these fabulous engineers did not fix the blind plug proper so a screw of the carburetor jets got lost. I fixed all that.
As result the engine works now in idle – no more backfire. But it takes very difficult throttle and the maximum power is much lower.
So I guess I need to adjust all carbs – right?
But how I do that?
Is there a basic setting for the carb jets – like close and then open 2,5 times – something like that?

I try to find a repair manual for that engine – but I could not find my type of engine.
Help is really very much appreciated.
Thank you

[twa2010]

Can someone please help me to find out what year is this engine?

[rodbolt17]

cant help much with the year, I dont have access to internatiobal engine information.
however the 3.1L engines are notorious for popping fuel pump diaphrams.
it also may be time to remove and clean the carbs.
but first your going to have to procur a Yamaha factory service manual.

[twa2010]

Prop slips or transmission?

Hi,
Thank you for your answer. What I learned so far is, that the last letter of the serial defines the year of the engine – in my case “P” equal 2004 – pretty good for me – it could be also 1998.
Carbs
Ok I cleaned the carbs. I worked out that they are not sync because there is baffle (part: bracket 3) between the two rows of carbs with lots of play. Means even during idle – one row is closed the other still a little open.
All jets I just open them 2,5 times, which seems to work.
Then I saw that there is oxidation under the coils – And that was the reason I was running mostly only on 4 to 5 cylinders instead of 6.
Next problem
After I try the boat know going maximum speed (55 mph) and accelerating a few times pretty strong – I lost propulsion - its looks like the prop is slipping. I lost power like the gear would be out. I hope it’s not the transmission.

It was pretty scary – to be far out and I could only go with 1.000 rpm back – otherwise no movement at all!
Does anyone have experience with this symptom?