Johnson 1999 90HP Runs Rough at low speeds

[Gary Mac]

Recently purchased a used 1999 Johnson 90 HP Outboard. It has been well used. It idles rough up through about 3000 rpm. Tried changing plugs no help. Even seems like it is missing around 2000 rpm. Had compression test - dealer says - OK. Should I try this decarbonization thing?? One other thing - it is on a pontoon boat. The oil tank is higher than the motor - I understand that is not good.

Any help would be appreciated
Gary Mac

 

[Robs88]

Re: Johnson 1999 90HP Runs Rough at low speeds

Has the engine sat for a while without use?

 

[Gary Mac]

Re: Johnson 1999 90HP Runs Rough at low speeds

Yes, I am pretty sure the motor has set without use for over a year. The model number of the motor is: J90PLEE.
Does anyone have think this decarbonization procedure would help or if even it applies to this motor. I do have an official Service Manual but read nothing in it about this procedure.

Once the motor get above 3000rpm the motor smooth out.

Thanks for all replys
Gary Mac

 

[tashasdaddy]

Re: Johnson 1999 90HP Runs Rough at low speeds

idle jets pickups are clogged, they pickup fuel from the bottom of the bowl. i had a problem with oil siphoning down into my carbs on my toon. i would relocate tank to the motor platform.

 

[Gary Mac]

Re: Johnson 1999 90HP Runs Rough at low speeds

Tashasdaddy - Thanks for the reply. Can I test out that theory by using a premixed fuel tank? If so how do I disable the VRO system.

Gary Mac