Why is my yamaha engine is running half power?

[josephhb]

i have a late 80 s early 90 s yamaha 175 ( precision blend ) outboard. i bought the boat with a new oil pump last year and it ran great. now its running half power and the bottom 2 plugs are soaked with oil and i dont smell any gas on them. they do have spark though!
Dead Sea 2u

[99yam40]

As always first off check compression on all cylinders and then spark with a spark tester to make sure it has good strong spark on all cylinders.
If all is good then look at the fuel system.
Post your model # and a little more on the history of what all has been going on, like when did it last run good,when did it start going bad, how longe between running, what you have done to it, etc.

[robert graham]

If you put a new/clean set of spark plugs in does it go back to running fine? If so, then you can start troubleshooting the reason for the fouled plugs on those 2 cylinders. Good Luck!

[awaikart]

The bottom two cylinders are fed by the bottom 2 barrel carb. I would suspect lack of fuel delivery from that carb. Try spraying ether in the bottom carb while under power and see if the power picks up. If it does the carb needs cleaning. As a rule of thumb all carbs should be cleaned at the same time.