9.9 carb issue

Hi all,

Right up front I do not have a Yamaha outboard, I have a Mercury 9.9 outboard. It is a 1996 "Bodensee" model and the engine was built by Yamaha, and the parts I have obtained for it have all come from Yamaha so I hope this counts. I have asked this on the Mercury forum a time or two and have not received a reply that has been of assistance so I am trying here instead this time.

So here is the problem. The motor will start on the first pull almost every time, and it starts idling just fine. After one minute, the rpms will start slowly increasing until they reach somewhere around 1500-1800. I can then turn down the idle speed adjustment screw two full turns and then I have a nicely running motor. I can run it all day, and I can start it and restart it. AS LONG AS I DO IT WITHIN ONE MINUTE. After that one minute, I have to adjust the idle speed adjusting screw back in two full turns and then the motor will start again just like at the start of this paragraph. And again, after one minute the rpms will start increasing blah blah blah. . .

There are no adjustments on the carb itself with the exception of this black electrical thing on the top. In the center of that there is a very small set screw and I can adjust that out to decrease the rpms a little, but not enough. I found the procedure to check the electrical component for proper operation and it works as described in the procedure.

I am at a loss so would appreciate any assistance you can give.

Thanks,

Wayne

1996 Mercury 9.9MLA4ST
Serial 0H008826

Re: 9.9 carb issue

possibly a bad electro thermal valve, possibly the carb needs to be dissasembled and cleaned.
there is an air/fuel adjustment screw, and the accelerator pump diaphram may not be working.
simple carb, lots of parts at the party, they MUST get along.
and yes the powerhead is 9.9 yamaha.

Re: 9.9 carb issue

I found it. It tuns out that one of the screws that I thought was fixed turned out to be an adjustment screw after all.

Wayne