2000 90HP 4 Stroke runs rough mid-rpms

[ddowis]

I bought a used 2000 90HP 4 stroke for my 24 foot pontoon boat. The motor starts and idles with no problem. The motor runs very rough between 2000 and 3000 RPM. At 3500 and beyond, smooth as a whistle. Any thoughts or ideas (other than don't run between 2000 and 3000 RPM) before a take my checkbook to my mechanic?

 

[ddowis]

Re: 2000 90HP 4 Stroke runs rough mid-rpms

I had my mechanic stop by and check the motor while boat was still in water. He said that only 2 cylinders are firing. He suspects that the carb is clogged and needs to be cleaned. I am pulling the boat this weekend and he will work on it next week. I'll let you know how this ends.

 

[DutchMerc]

Re: 2000 90HP 4 Stroke runs rough mid-rpms

This could be an ignition problem... Check if all sparks are there, check if the sparkplugs are in good shape. ( dry and correct collor).

 

[ddowis]

Re: 2000 90HP 4 Stroke runs rough mid-rpms

Thanks, I'll check that first.

 

[hamit59]

Re: 2000 90HP 4 Stroke runs rough mid-rpms

It's a carbed 4 stroke you could run sea foam through it to see if it will clean up your high speed jets. But being a 4 stroke Any good carb cleaner, might clean them up. I would load a remote tank up run it while it's in the water.

 

[ddowis]

Re: 2000 90HP 4 Stroke runs rough mid-rpms

Thanks. I use seafoam in the tank as a stabilizer all of the time. I will try a carb cleaner.

 

[ddowis]

Re: 2000 90HP 4 Stroke runs rough mid-rpms

I took the boat to my mechanic over the weekend. He called me today to tell me that one of the carbs was completely clogged....with salt. He says that it doesnt appear that the engine has been submerged, but it definately had salt water going through the carbs. He is pretty confident that he can get it cleaned up. More to come...like my conversation with the guy that sold me the engine.

 

[ddowis]

Re: 2000 90HP 4 Stroke runs rough mid-rpms

Got the boat back from my mechanic last weekend. All of the carbs were badly clogged (not with salt). Cleaned all carbs, new plugs, new water pump, new lower unit oil. $325 and it runs like a top.