199? 115 Merc 4 cylinder, possibly late 80's carb help needed

[lmuss53]

I am working on this 115 Merc, late 80's early 90's vintage, SN 0D106981, 4 cylinder oil injected. When I got it it would not take any throttle and was idling very rough. In another thread we did some trouble shooting and decided to change the melted down CDI and the voltage regulator/rectifier. The idle immediately smoothed out and the motor seemed like it was raring to go. We took it over and it idles right now, but still won't accelorate when you give it the throttle. Little bumps on the enrichener gave it little surges of power, pumping the ball and a different fuel line/tank combo made no difference, so we decided to clean the carbs.

I took them off and laid them out on my bench like I have with a hundred other sets of carbs. I stripped them down to the individual parts and got them soaking in the cleaner. I got online and ordered the needles and gasket sets. THEN I looked at my online manual for theses carbs and saw that the screw in the picture below is NEVER to be removed once it leaves the factory. The sealer had been removed from these long ago and I must assume that someone else had them out at some time. They all seemed to be about right at a light touch to the seat when I checked them before removing.

So my question is, can anyone tell me how to reset them, or is there an "approximate" place to start with them? Once they are back in is there a way to check to see if they are doing what they are designed to do? It looks like they vent the carb to the atmosphere, perhaps at idle. Help me if you can, I am trying to put this back together and am not sure what to do with these.



Screw and spring go in this threaded hole.




Better view of the carb.

 

[flyingscott]

looks like a 92 model and I believe it's a 2+2 motor. That means the carbs WITH the idle circuits go on the top 2 cylinders and the 2 without go on the bottom Take a pic of what screws into the hole.

 

[lmuss53]

Yes it is a 2+2 motor, having idle adjusters on only the top two carbs, however these screws are on all 4 carbs.

 

[lmuss53]

This is how I got the carbs, all the sealer had been picked out and the screw was lightly seated, not at all tight, and maybe even open a crack. The owner bought the boat back after having previously owned it. It has never run since he got it back, and now I'm wondering if these adjustments are way off, causing the problem all along. Someone may have messed with them, trying to "adjust" the carbs, gotten it all out of whack and just sold the boat.

 

[flyingscott]

I would call mercury. Do you have the factory service manual? that is a must have for that motor

 

[lmuss53]

The factory manual is where I found the information I have. It's where I read that the screw should never be removed, it is set and sealed at the factory. The sealant was out of these, and I treated them like any other adjustment on the carb. I turned them in until they stopped, then backed them all the way out to clean behind them. They were mostly in against the seat, but not tight, maybe a quarter turn away from the seat. I got the manual out to see how close the idle screws were to the recommended starting place, then I saw that the brass ones were to remain sealed and not to be removed.

 

[flyingscott]

I would call the Mercury home office for tech support..

 

[Faztbullet]

They are set 1/4 turn out from a light seat per factory manual...

 

[lmuss53]

I see that for the idle screws, but the only thing I see for these screws is to never mess with them. That would be about where they were.

 

[lmuss53]

Faztbullet, I sat down and read the entire section after your post, lo and behold, there it is for all to see. Thank you for taking the time to point me in the right direction. I will set them to 1/4 locktite them in place and never touch them again. Again, thank you sir.

 

[lmuss53]

It's a little stumbly on the idle but the 2+2's are like that and I set the screws a little on the rich side like the manual says.The holeshot is a little flat, but the holeshot is partly because of a 23p prop on an 18 foot fiberglass boat with the 115 hp. It tachs out at 4500 rpms at wot. I told the guy I would put a 19p prop on it if it were mine. he says he will try it out as is and let me know.

Thanks for the advice on the screws, this is the best outboard forum there is.

 

[flyingscott]

Your operating range is 4750-5250 rpm that motor is overpropped.

 

[lmuss53]

Yes sir, I convinced the guy of that, we are looking for a 19P.