engine problems 40 hp outboard

[pauldwd1]

I have a yamaha 99, 40hp tlrx. While running at full throttle the rpm drops to less than 2000 rpm. If I back off the throttle it will run fine for a period of time.And then the problem reoccures. I have done all that I can think of. I did the following one at a time and the problem continued. Changed gasoline, hoses, spark plugs,had the carbutetors cleaned, replaced both heat sensors even though the engine temperature appeared to be fine. I now think the CDI is the culprit. Has anyone run into a simular problem and if so did changing the CDI correct the problem or how did you correct the problem? Because of the expense of a new CDI, I don't want to change it if it doesn't correct the problem.

[boats.net]

It sounds like a fuel problem, check fuel tank vent when it drops rpm's loosen gas cap if it picks up rpm's the tank is not venting. you can check for fuel restriction with a vacumn gauge. I have even seen the fuel filter installed upside down and restricting fuel flow.

[pauldwd1]

thank you for the reply. I checked the fuel vent and also changed fuel pumps. in addition i replaced the water pump. still have the same problem. thanks, paul