carb problem on 1996 Merc 9.9

[xeddog]

Hi everyone.

I asked the following question a few months ago before getting side-tracked by having to replace the engine in my boat (again). But . . .

I have a 1996 Merc 9.9 Bodensee outboard motor (long shaft if that matters) that I want to use as a trolling motor. This motor is apparently a sort of a weird one for Mercury, and it is built by Yamaha. To get carb parts, I have to go to a Yamaha specialist because most carb parts are not available from Mercury.

Anyway, the problem is this. When I start the motor cold, I have to turn the idle speed adjusting screw in two full turns. When I do that, the motor will start with just one or two pulls on the rope, and it will idle nice and smooth. But after a minute or two, the rpms will slowly start increasing to the point that after about 5 minutes it will be running at somewhere around 2000 rpm. Without a tach it is hard to estimate the actual rpm, but it is WAAY to fast to troll with my 21.5' boat. I can then turn the idle speed screw back out two full turns and it seems to run fine again. If I shut the motor down, it will start back up with one pull PROVIDED I restart it within one minute. If I don't get it started that soon, I have to leave it for a least 3-4 more minutes, turn the idle speed screw back in two turns just like a cold start, wait for the rpms to stabilize again, and then reset the idle speed adjusting screw again.

This carb has no choke in the traditional sense of a restriction in the airflow path to cause the mixture to enrich. There is a black electronic thing on the top of the carb that is about 1" in diameter and maybe 1.5" tall with two wires coming out of it. If I remove this thing, there is a small brass rod (maybe 1/16" dia? and maybe 3'4" long) sticking out the other end that looks like it could open or close a fuel passage. I don't know what this thing does, but I do suspect it since everything else looks to be ok. All clean and free movement.

I can't think of anything else that I think is relevant, so I am open for suggestions. Any and all comments welcome.


Thanks in advance, and sorry for the length of the post,

Wayne

 

[Coloradolakeboy]

Re: carb problem on 1996 Merc 9.9

Hey Wayne, look at the stickys at the top of the first page of this forum. You might be able to look up the service manual for your motor. At the least, I have bumped up your question, hopefully someone here can help.

 

[xeddog]

Re: carb problem on 1996 Merc 9.9

Thanks for the info regarding the manuals. I had tried to d/l them once before but needed a password. I found the password today so I downloaded a manual. That electrical thing on the carb is called a "Starter Set" which sounds interesting, and there is a procedure to test it. Kewl.

Wayne

 

[CharlieB]

Re: carb problem on 1996 Merc 9.9

That 'Starter set' is supposed to work as a fuel enrichener when cold. Once the motor starts the charging system energizes that coil and is supposed to close the fuel passage.

Since you are turning in the mixture screw the system is not functioning correctly, the service manual should spell out how to test, clean and get it back in order.

 

[xeddog]

Re: carb problem on 1996 Merc 9.9

Thanks CharlieB.

I did the tests outlined in the manual and the starter set passes. One of the tests was to connect it to a battery and "Wait for several minutes". I did that, but since you have to have it connected for several minutes, and it takes several minutes for the problem to fully develop when the engine is running, that is no coincidence. I think I need to go back and check all the wiring again. Maybe it is not getting current.

Wayne