Yamaha F9.9 4 stroke 2017 loss of power

[timroving]

Hi all and thanks for reading this. I have a Yamaha F9.9 4 stroke 2017 outboard motor that has been running sweet until recently it started losing power. It has always been serviced at Yamaha. The motor has under 100 hours. I am a retired car mechanic. It starts fine and idles well but now will not get to full power or on the plane. It does not miss or sputter just has low power and not teaching full revs under load. The hull is clean, the propeller is free, I have changed the plugs, checked compressions, changed the fuel filter, removed and cleaned the carburettor that was very clean inside, checked the oil level and changed the fuel, checked the connections are fitting correctly. The timing belt looks fine and has the correct tension. The warning light works on starting and is not coming on when running. I have primed the hand fuel primer whilst running to check the fuel pump is working OK. I have searched the internet with no results other that the below video that looks like the same symptoms. To me it’s like the timing has moved or changed electronically. Can anyone suggest anything? Thanks. Tim

https://www.youtube.com/watch?v=67iZz0TY-wY

[MicHughV]

Though you took the carb off and cleaned it, there is likely a spot somewhere that you missed..as it sounds like a fuel starvation issue to me as the engine is not reaching it's full operating rpm.

Just a thought....those little carbs have a tiny mesh screen somewhere, it's hard to see, as the screen can get dirty and you wouldn't know there was a screen there at all...it is small....top of match stick size....with a very fine mesh...it's a problem made worse by the use of ethanol laced fuel.

Failing that, you could take the carb to a shop where they can soak it in their propriety carb cleaning solution...which is what I have done in the past, faced with a similar situation as yours. This usually always does the trick

[timroving]

Hi, yes although I had cleaned the carb before I did it again and soaked it it as well, didn't find any thing, spacer correct way round and the same problem. Starts well and revs OK in neutral but in gear it seems bogged down and won't rev over it seems like 3000rpm. Changed fuel lines from the tank, no difference. The belt timing is OK, cleaned out and checked the thermostat, OK. Can the CDI give this effect of good starting and idle but low top end power?

[MicHughV]

I can only relate to my own experiences, so without seeing your engine, I still think it's the carb.
Like you, I tried cleaning my own carb, soaked it some carb cleaner liquid overnight, but the problem remained.
I ended up taking my carb to a local outboard repair shop.. they took it apart and soaked it in some stuff that they had, that the average joe in the street doesn't have, and voila, that did the trick.
Some of those holes, jets, etc in those small carbs are really small.
Could be the float setting, another small item, that can restrict gas flow

The only other possible thing I can think of, is the throttle linkage, does it open the carb all the way, when you twist the grip.

Besides that, nothing else springs to mind.

[MicHughV]

I should add that the outboard shop use a high pressure air hose to blow stuff out, most people don't have access to such a thing...