Mercury 90 4 stroke wont run abouve 3500 RPMs

[sigmawess]

I have a 2007 90 HP 4 stroke mercury. I am only getting power at half throttle. At full throttle it wont rise above 3500 RPMs and it takes forever to plane. The motor only has 35 hrs on it and before this ran 6500 rpms at full throttle. My father says something is worng with the O2 sensor not allowing enough oxygen to mix with the gasoline. Any ideas?

 

[Faztbullet]

Re: Mercury 90 4 stroke wont run abouve 3500 RPMs

Without the serial number it hard to say but if it has carbs and has been setting I would say carbs need looked at. Do the basic checks first for spark and compression and check fuel for seperation and water. A EFI engine will have a O2 sensor and it basicly O2 moniters the exhaust gas and tells EMM if the engine is too rich or too lean.

 

[sigmawess]

Re: Mercury 90 4 stroke wont run abouve 3500 RPMs

Its an EFI

 

[Faztbullet]

Re: Mercury 90 4 stroke wont run abouve 3500 RPMs

Thanks for the addition info.... check the spark first and then the plugs for fouling. On the EFI engine it could be a fouled plug,clogged injector/s, shift interrupter misadjustment,defective oil pressure switch, pulsar coil or engine temp sensor.