Mercury 115 2+2 How smooth should this idle?

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cps22

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I have a 2005 115hp 2+2 Merc, probably one of the last one's made, just my luck.

This motor runs great, but starts & idles poorly.
Last year my wife and I put on over 800 miles averaging about 3.5mpg per the GPS on several of the Southern waterways. Above idle, this motor runs great, never a miss, sputter, etc.


Its cantankerous when starting, sometimes at the touch of the key, other times it may take several attempts, never predictable, warm, cold, unpredictable starts. Sometimes it idles good, sometimes(usually) it doesn't. Seems like it runs rich at idle, some noticeable blue smoke.

The question I have is how smooth should this engine idle? What are the experiences of other owners of these 2+2? Did Mercury make a motor that idled so poorly, or is it just mine?

Things I've tried: (note this was before the 800 mile run last summer)
Removed and disassembled all 4 carbs( I know, only 2 have idle adjust) blew air through every visible passage way, adjusted the floats, put all back together.
Adjusted the idle screws many times, seems like 1 1/8 to 1 1/4 works about the best.
Motor runs well, just doesn't idle smooth, and starts hard.

The one other observation is that the type of gas seems to make a difference. I'll generally fill up before going to lake/river while boat is still on trailer and its likely that it's gas with the ethanol mix. Later that day while on the water I'll fill up at a marina and I believe the gas doesn't include ethanol, and/or may be a premium (sure costs more). Idle often needs adjusting after a fill, other times no difference.

I noticed in the shop manual that there is a oil injection pump adjustment but it doesn't seem to be clear to me. Anyone have suggestions on if oil pump needs adjusting and how? Again, there seems to be blue smoke at idle at times, but not all times?

So spring is around the corner... anyone have suggestions?

Thanks in advance, CPS22
 

Crazy D

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Re: Mercury 115 2+2 How smooth should this idle?

If you are blowing smoke i'm guessing you have too much oil in the mix . Your motor is oil injected , so i would have a mercury tech check it out and make sure you are getting the correct oil/fuel mix .
 

Silvertip

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Re: Mercury 115 2+2 How smooth should this idle?

Two strokes smoke -- period. You can reduce smoke by using a semi-synthetic or full-synthetic two stroke oil. Adjustment of the oil injection pump is likely not necessary and if you insist on doing this, follow the instructions in the service manual. Starting issues are generally operator error. You didn't indicate what your starting procedure is. If its get in and turn the key -- that would be the wrong answer. Don't blame E10 fuel. Judging by the other things you've said I think you don't have the carbs adjusted correctly. filling up with E10 or regular gas would not immediately affect idle quality since whatever you added would have mixed with what was there. Idle mixture affects ONLY idle and off idle (transition). As for smoothness, A four cylinder engine firing on all four cylinders is going to be smoother than a four cylinder engine firing on only two so there will likely be a difference if you compared it with a non-2+2 motor. There is no straight answer for that question since what is smooth and acceptable to one person is rough and unacceptable to another.
 

CharlieB

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Re: Mercury 115 2+2 How smooth should this idle?

Many owners of the 115 2+2 do not relize the motor only idles on the top two cyls.

Idle mixture is critical, start at 1 and 1/2 turns out from lightly seated, start and warm up the motor securely tied to the dock.

Once warmed up, shift into Forward gear and adjust idle mixture to BEST idle speed while in gear.

The top carbs do NOT have the acccelerator pump and the idle mixture MUST BE adjust slightly richer than 'Best Idle Speed' to provide the additional fuel necessary for acceleration. Adjust the idle mixture screws OUT just the bladewidth of the screwdriver slot on the mixture screws.

Test acceleration by rapidly opening the throttle to WOT. This might be better done out on the water than still tied to the dock.

ANY lean cough, bog, or hesitation the mixture is still too lean, open the idle mixture screws another bladewidth and retest acceleration.

Repeat to perfection.
 

Silvertip

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Re: Mercury 115 2+2 How smooth should this idle?

Setting idle mixture screws and throttle response out of the water is not acceptable because there is no backpressure on the exhaust. To set things properly it must be done in the water or at least a test tank.
 

cps22

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Re: Mercury 115 2+2 How smooth should this idle?

Thanks everyone for your responses.

Not sure I got the responses I was hopping for...

The question I have is how smooth should this engine idle? What are the experiences of other owners of these 2+2? Did Mercury make a motor that idled so poorly, or is it just mine?

I am aware that idling occurs only on two cyls.
One response asked about my expectations about starting. I expect that a motor that was run for an hour, then stopped for 5 min, would start with just a turn of the key. I would expect it to start harder if it had been sitting for a couple of days. My motor is very cantankerous, sometimes warm starts are just a turn of the key, but most often not.
I've adjusted the carbs often, it idles good for awhile, only to idle poorly later that day.

Again, the only symptoms I experience is rough idleing, and hard starting. The motor runs flawlessly, accelerates perfectly, even at WOT, although I don't often push it that hard.

So, although its a judgement call, do your 2+2 Merc's idle OK? Just trying to get a concensus.

Thanks CPS22
 

Silvertip

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Re: Mercury 115 2+2 How smooth should this idle?

You are very mistaken about starting of a two stroke with "just the turn of the key" after sitting for an hour. If you ran the boat hard, shut it off abruptly and then tried to restart an hour later chances are it would start differently than if you puttered around for awhile, idled up to a dock and then shut the engine off. That engine like most two strokes, has a fast idle lever on top of the control box. Learn to use it. Ambient air temperature and humidity can also affect how a carbed two stroke starts when warm and cold. This is not a one technique fits all circumstances. That engine like most two strokes, has a fast idle lever on top of the control box. Learn to use it. I will assume you know about the "push to prime" situation so that too may be necessary even after sitting for just one hour. Just a touch perhaps, but priming (choking) may be necessary nevertheless.
 

simms71

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Re: Mercury 115 2+2 How smooth should this idle?

I have owned a 96 115 merc for 4 yers now. I have come to the conclusion that this engine is a bad idler. Runs great out of the hole and pushes my ranger very well. But, no cleanning no additive no adjustment fixes the idle problem. I just live with it. others I have spoken to have had the same comments about this 4 cyl engine idleing on two carbs. Great running engine, just a bad idler.
 

elan86

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Re: Mercury 115 2+2 How smooth should this idle?

My 1988 100 2+2 idles awful. Rebuilt carbs and fuel pump, adjusted carbs. Will try to tweak the idle mixture like was said above. Mine runs very well at cruising speed, holeshot is tentative. Bog then release of power. Silky smooth at cruising speed but when I go to low speed or idle it wants to stall. On muffs at the house it starts ok, usually after 2 choked turns of the key. Runs ok then starts surging then sputtering, surging then sputtering.
 

cps22

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Re: Mercury 115 2+2 How smooth should this idle?

Simms71 & Elan86;
That is the information I was looking for. Sounds like this is and has been a wide-spread problem for years and is a basic quirk of this type of engine. I was concerned that only I was experiencing this rough idle problem. I too agree with your comments that at above idle the engine runs great. Guess I'll have to learn to live with the rough idle or upgrade this boat.

My problem is also related to what I'm used to on my other boat; I have a Merc 115 4-stroke on my pontoon and its the smoothest, quietest, best starting, economical engine I've ever had.

Thanks for everyone's inputs.

CPS22
 

gbrowne9

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Re: Mercury 115 2+2 How smooth should this idle?

i too have a rebuilt 115 2+2 and i find to start it the fastest is by priming the bulb hard,push in the key while turning the engine over.once started pull up the warm up lever.you still may have to tap the key in every now and then to keep it running.from warm start i just push the key in while starting,works every time.my mixture screws are set at 2.5 turns out.my motor is a 1988 and it idles a little rough but it always runs.i disconnected the oil injection because i was leary about it.its a good engine,great on gas and quiet
 

Napoleon

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Hi gang,
It’s been a while since the last post, but here’s what I’ve done to remedy the rough idling issue on my 1996 Mercury 2+2.
I bought 4 used carbs on e-bay, bought 2 carb kits ( which included new idle jets). I did not use the 2 upper carbs, but the two lower ones because of compatibility of the fuel inlet connections.
I bored out with mini drill bits ( took a dismantled top carburetor to a tool shop and purchased 2 bits..one for the choke fuel entry and another to enlarge the current oil orifice in the choke chamber that pours into the air/fuel venturi+ drilled a new orifice ...just like the ones on the top carbs.
The new idle screws fit perfectly on these lower carbs.
Adjusted the idle screws to 1 -1/4.....guess what, after some minor tuning of the idle screws, I’ve got the smoothest idling 2 stroke...I now call my Tasmanian devil...Sayonara 2+2
This also increased my idle speed by 400 RPM, + also 400 Rpm at the top end, which now reaches 5200 RPM, because of the extra fuel from the lower carb idle orifices.
The oil injector system has been removed and I Use 50:1 miixture ( full synthetic 2 stroke Amzoil)
Comments?
 
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