1990 merc 115 2+2 elimination

[sboyd79]

Hello, I have asked a few merc guys about removing the 2+2 from my mercury. I am told that the difference is in the carbs and all I need is 2 carbs from another motor(which is what I have), or buy the carbs somewhere and switch the 2 out. I have my motor that runs on the boat, and a complete blown parts motor. I just want to confirm which 2 carbs don't run at low rpms. I have seen other threads where people have done this and they are much happier without the 2+2, I myself do not like the way it runs now.

 

[Laddies]

Re: 1990 merc 115 2+2 elimination

Mercury didn't build that engine that way without a reason, with 4 carb to idle on it will not go back to idle speed once it's on the pipe all the time

 

[MercGuy]

Re: 1990 merc 115 2+2 elimination

The bottom 2 carbs are the ones that would need to be replaced (they do not have low speed jets).

If you try this, please post your results. I would be very interested to hear how it works. I've read many opinions on whether this would work or not, but I don't ever remember hearing from someone that actually did it.

I have a 1998 115 2+2 and for a time I hated the 2+2 design and wanted to do what you are suggesting. Since then, I learned and fiddled and now mine runs great and I'm happy with the way it runs.

Here are my tips for making the 2+2 run well:

1) Do a complete link-n-sync per the manual to assure that everything is set up properly

2) Do a decarb

3) Prop your boat so that your running at 5250 RPM (or very close to it) at WOT. These engines do not like to be lugged, and being over propped makes it more difficult to switch from 2 to 4 cylinders.

4) Gap your plugs at .032 instead of .040 as the factory suggests.

After doing these 4 steps, my engine runs great. It rarely misses or stumbles when I put the hammer down. 99% of the time it just pops from 2 to 4 cyls, with an authoritative bite. Of course if I hang around 2000 rpm it stumbles and misses as it alternately runs on 2, 3, and 4 cylinders, but that is the design and is to be expected. On my setup the boat is just crawling up on plane at 2K rpm, so I would never hang there anyway.

Let us know what you find. If I had the extra carbs sitting around I'd do it just to find out if it works. Wouldn't take much to switch it back if you didn't like it.

 

[sboyd79]

Re: 1990 merc 115 2+2 elimination

Hi, thanks for the replies. I see adjustable idle screws, so I'm not sure how it will idle, but I think I'll try it, like Mercguy says, I can always put it back. Any more comments or advice out there would be appreciated just the same, especially if you have done this switch over before.

 

[CharlieB]

Re: 1990 merc 115 2+2 elimination

The only problems I've seen on this syem is the carb sync and idle mixture adjustments on the top two incorrect.

Dialed in this works.

This is Merc response to EPA mandates to reduce idle emissions.

Check the cars, you are beginning to see more 'variable #' of cylinders, cylinders shut off when NOT needed.

The Merc system is simply NO fuel to the bottom two cyl's it idle. Period.

The moment the throttle plate opens fuel begins to flow, and the lower cyl's are running.

Acceleration requires a fatter mixture so Merc provided an accelerator pump on the lower cyl's for rapid throttle openings.

Dialed in correctly the systems works.

Removing the accel pump and replacing the lower carbs more or less converts the engine to an old sytem which also works IF it is adjusted correctly.

The only negative to the conversion is the increased fuel use if idled much.

 

[MercGuy]

Re: 1990 merc 115 2+2 elimination

Hi, thanks for the replies. I see adjustable idle screws, so I'm not sure how it will idle, but I think I'll try it, like Mercguy says, I can always put it back. Any more comments or advice out there would be appreciated just the same, especially if you have done this switch over before.

Just a quick comment. The "idle screws" you see on the top two carbs are not for adjusting idle speed. They are for fine tuning the fuel mixture, and will affect how smoothly the engine idles, and they have an effect on if it stumbles during acceleration.

Idle speed is contolled by a finger screw on the throttle arm (it should be clearly marked with a sticker).

 

[MrLundt]

Re: 1990 merc 115 2+2 elimination

I have seen other threads where people have done this and they are much happier without the 2+2, I myself do not like the way it runs now.

What is it that you do not like about this system? I have a 1988 100 h.p. 2+2 system. One year the needle valve in the #3 carb was stuck and this year I had to dip #3 and #4 to clean out the jets but for the most part, it runs well and has not needed a lot of tweaking. I was just wondering what you did not like about your motor or what you are hoping to improve after your modifications. I, too am interested to hear about your results.

 

[sboyd79]

Re: 1990 merc 115 2+2 elimination

Hello again, I appreciate all the feedback given. I simply do a lot of just over idle cruising. We spend a lot of time in the finger lakes & lake ontario looking at the trees and shore line at this time of year. Or when I come down in throttle coming in out of the lake, I sometimes have to slowly cruise up river a ways with no wake, depending on where I launch. I also go to the many adirondack lakes. The erie canal also is a 6mph max, so there are many"just over idle" situations I get into and it seems I'm right in that 2000 RPM range. It seems to load up a little, and sometimes sounds like it trying to fire on the other 2, if I get the speed just right. I see a lot of the adjustments mentioned in this thread and I'm trying to mess with it a little before I change the carbs. I just simply have a blown parts motor and knew I already had the carbs, and just thought it would run better that way-like the old way. I let you guys know what happens with my situation. Thanks again for all of the input, and of course, more is always welcome.

 

[weetee]

Re: 1990 merc 115 2+2 elimination

How do the off cylinders stay lubed if they are fuel/oil starved?

 

[clevecan]

Re: 1990 merc 115 2+2 elimination

well my 1988 100HP merc runs great at WOT but the way it runs in the wake zone I hate! bout ready to sell it, A real bummer to I like the way it runs other than that prob.

 

[The_Kid]

Re: 1990 merc 115 2+2 elimination

How do the off cylinders stay lubed if they are fuel/oil starved?

The bottom two carbs do allow some fuel flow during idle and up to 2000 RPM, but just enough to keep the cylinders lubricated. The fuel to air mixture is to lean to support combustion. Since the fuel and oil mixture is not burned, everything stays lubricated.

 

[clevecan]

Re: 1990 merc 115 2+2 elimination

so on my 2+2 100HP which carbs work at low rpm's Can I just ajust the top ones while in gear in the water on the ramp? am I looking for peek idle speed while ajusting them, will this also help the stumble at the hit of the throttle.