100 hp Mercury from 1996 problems

Question
I have a 2 stroke Mercury 100 hp ,  4 cylinders in line . I ran 2 weeks ago in dirty water with it and the cooling system was blocked. The motors runs like that for 5 minutes when suddenly it goes down to 2000 rpm and from then the motor won't accelerate more than 2000 rpm . It works fine , idle well but no more than 2000 rpm . I cleaned up the cooling system , it works very good with new propeller . Thank you , radu

Answer
Hi Radu...Thank you for selecting the undersigned to reply to your question. By the way, I'm not a mechanic.

First of all, the engine is obviously not working "fine"!

I'm not certain what you meant by cleaning up the cooling system, and that "it works very good with a new propeller". Your symptoms do not indicate a problem with the propeller.

Did you concentrate on the water intake aspect? Often, the impeller can become damaged by foreign materials/objects entering via the water pickup port, which in turn can and will restrict the flow of water throughout the powerhead, thus causing overheating. Did you check for contaminated or low octane fuel, or a defective fuel pump or fuel line?

Best you consult a qualified and reliable marine mechanic to diagnose the symptoms and resolve. It may be cheaper in the long run.

Safe Boating
Ron