85 Yamaha 40hp

[Jman31600]

Motor will not get up too speed. Max speed I've got is 9mph, took the boat in and they checked it out and without a dyno test they couldn't find anything. Good compression, new spark plugs, new fuel lines, prop is good. When I have it full throttle 2600 rpm is the max. It seemed like it would never plane out unless somebody sat in front and it got level. Any ideas somebody would have would be great. Thanks in advance.

 

[tommarvin]

Sounds like dirty carbs, I would drive further to the next certified Yamaha outboard mechanic,and get the dyno test

 

[99yam40]

need good compression and good spark at the correct time along with the proper fuel to air ratio in the cylinders to run properly.
so far you said they only tested compression.

Test what you can and then look into the stuff you cannot test.
fuel pump leaking into crankcase will cause too rich of a mix in #3 cylinder

 

[tommarvin]

Are the throttle butterflies horizontal at wide open throttle, test with the motor not running, put the throttle at full throttle look in the carb throat with a flashlight,
Remove and clean all the openings in the carb(s) with carb cleaner, and blow with compressed air