My 9.9 HP '92 Mercury motor runs great at first, but then slows down?

[BillDance32]

The first time I crank up my 9.9 HP Mercury motor, it runs absolutely flawless and cranks up with ease. The motor runs great no matter how long or far my first trip to a new location is. Then problems occur after I kill the motor and turn it back on later. The next time I crank up the motor, and every time the rest of the day, the motor will run at about 20% of speed it was during the first run. I then have to slowly move around everywhere throughout the body of water.

It's the strangest issue that occurs EVERY single time I go out. The motor runs flawlessly at first and starts up with ease. Then once I shut it off and try to run it again, it runs terribly and slowly. The only thing I really notice is that it makes sort of a high pitched noise when it runs slowly, it's almost like a rattling, or sounds like it isnt getting enough gas, but I'm pretty certain it is. I've asked this question in previous years and even taken it to get fixed, but nothing seems to solve the issue. Any thoughts are greatly appreciated.

I use a 50:1 oil ratio and its a 2 stroke.

 

[CharlieB]

Re: My 9.9 HP '92 Mercury motor runs great at first, but then slows down?

First check the fuel tank vent, make sure it is open and clear.

Second, how long since the carb has been cleaned? Most the 9.9's have an automatic choke, once it gets too dirty it doesn't want to open/close properly.

Do you have a factory service manual. It will become your boating Bible, spelling out how each part fits, take it apart, clean, reassemble and adjust following the directions.

If you do not have a factory manual post your model and serial. One of the guys will point out exactly which manual is for your motor.

It will be the best book you've ever bought.