engine drops when giving throttle

kloost12

Recruit
Joined
May 17, 2015
Messages
2
Hi all,
i just bought a very nice boat with a Yamaha four stroke outboard engine, F9,9CE (66N A0). But unfortunately the engine is not running as it should. It doesn't run smooth and in my opinion the fuel mixture is too rich or to lean. the airfilter has been taped for 40% and the air screw is pretty far open. This only must be 1,5 turns, right? (now almost fully open). When you give throttle, the engine drops. if you carefully give throttle, then it will go up.

the airfilter, should not been taped and the air screw not wide open. So i am wondering what is wrong.

1. Could it be the fuel pump?? maybe i have to change the diapragma? There are no holes in it, it only ribles a little bit, like the rubber is not flat/stiff anymore at that point. Maybe that is the problem, since the suction is not that strong now?? could this be the problem??

2. or could the problem be at the electric shoke? maybe that one is broken and just gives too much fuel continuously? can i check this? and how?

any other ideas?

i checked all the fuel lines and changed the fuel tank and the problem still occurs.

Hopefully somebody can help me out!

thanks in advance!

gr. Rutger
 

kloost12

Recruit
Joined
May 17, 2015
Messages
2
Thanks, but that is something i already did and the problem still occurs. Thatswhy i thought it could maybe be the electronic choke or the fuel pump. any advice is much appreciated. thanks.
 

99yam40

Fleet Admiral
Joined
Sep 7, 2008
Messages
8,851
there is no air filter on an outboard that I have ever seen unless someone added it.
If they taped off some of the opening on the silencer to make it run so they could sell it, there is no telling what all else they have done to the motor.
All you can try is to get it back to factory specs, what ever that takes

check compression, spark timing and set everything to factory spec. A service manual for your motor will help do these things
 
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