1999 Merc 115 Outboard idle question

[rockbill823]

My 1999 115 Mercury outboard has a feature that when it is run below 2000 RPM it goes into a low speed mode running on 2 instead of 4 cylinders which resembles a miss. I know this is designed into this model for low speed trolling, etc. What is actually happening - does the control unit turn off the spark in 2 cylinders, does fuel get shut off? Is there a way to disable this feature? Do I just live with the rough idle?

 

[fatpratt1996]

Re: 1999 Merc 115 Outboard idle question

By what I've been told, there are only two carbs with idle circuits. Around 2000 the other two kick in, assuming you have a 4 cyl like my 125. My engine seems to idle o.k.. Only when the second two carbs are just kicking in is when it is rough(feels kinda like a miss) but when thay are activated she runs good. Not a good trolling engine but what can you do?

 

[Clams Canino]

Re: 1999 Merc 115 Outboard idle question

Originally posted by fatpratt1996:<br /> Not a good trolling engine but what can you do?

You can get a 1988 115 instead and have it all. <br /><br />-W

 

[fatpratt1996]

Re: 1999 Merc 115 Outboard idle question

good point. I purchased my 125 without doing any "extensive" research on it. I don't troll much though so "It don't bother me none." Let's go fishin

 

[Boatin Bob]

Re: 1999 Merc 115 Outboard idle question

I've got a 2003 115hp Classic and asked this question before, the answers varied but for sure you need to replace the bottom 2 carbs to match the uppers so you get the idle circuits. Apparently the existing carbs allow just enough fuel through for lubrication but not enough to fire. I don't really like the feature but wanted the max hp (115) for my boat for skiing and wakeboarding. Never checked into the price of the carbs but i'm sure they would be cheap

 

[WillyBWright]

Re: 1999 Merc 115 Outboard idle question

They did that because they couldn't get a decent idle. The 75/90's idle real bad! The prototype 100/115/125s idled much worse. Changing to all-same carbs won't give you anymore horsepower and you won't be able to manage your idle speed...it'll always idle way too high. The throttle plates have holes in them to manage the idle speed rather than cracking the butterflies like everybody else on the planet does. The holes are fairly large to make it idle on two. Add two idling carbs and your idle RPMs will about double.

 

[SingleShot]

Re: 1999 Merc 115 Outboard idle question

I have the same 2003 classic 125, it took some time on a stock tank filled with water to get the carbs adjusted just right, but I get a good enough Idle to troll around 2 to 2.7 mph on my gps for a couple of hours with out problems. I don't troll much but when I do it does an OK job.<br /><br />JK

 

[Clams Canino]

Re: 1999 Merc 115 Outboard idle question

Not to belabor the point, but I find the fact that the Mercury marketing boys used the word "Classic" to describe the current crop of carbed 115/125 2+2 critters to be shamefull.<br /><br />-W