9.9 Johnson bogs at WOT

[csj59]

I have a 99 Johnson 9.9 outboard. When first started it fires right up and runs fine but after it warms up it bogs down under WOT. If I remove the engine cover it will run fine. I already took the carb off and went through it and checked the fuel filter, there are no signs of contamination. I dont think it is spark related, what could the connection be between cover on and cover off.
Thanks for any help

 

[SKEETR]

Re: 9.9 Johnson bogs at WOT

That usually indicates an exhaust leak of some kind messing with your fuel/air mix.

 

[csj59]

Re: 9.9 Johnson bogs at WOT

What is the best way to test your theory. I have been an auto tech for 25 years so I know my way around autos but know very little about boat engines

 

[Silvertip]

Re: 9.9 Johnson bogs at WOT

Very likely the base gasket between the power head and lower unit. Exhaust gas with the cover on is being sucked into the carb.