loss of power

[Bike4mee]

Hi. I'm new to site. I have a 40HP yamaha outboard on a Avon inflatable. Not sure age but model 40MLHR IS ON IT. It starts and runs fine but at top speed (or lack of it) it will plane out then drop suddenly with a loss of power. Then it goes again and planes out, then drops. Sometime I cant even get it up to speed. The funny thing is if I pull the choke out a bit it runs real fast again with just a miss not smooth but fast. Any ides?

 

[99yam40]

carbs need cleaning if choke helps.
take a look at the fuel pump also

never hurts to check compression on all cylinders
spark on all plugs,'
and timing too