Mercury 115 2+2 questions

[ohmthis]

hey guys and gals,
I just completed my full rebuild on my 1990 115. I know it has a 2+2 ignition setup, is there more info on tricking the factory ignition? I haven't even gotten past the 2 hour mark, but I can tell it doesn't have that much balls down low. It is on a 19' fish and ski, and it will be used more for ski than fish.......So I need all the hole shot I can get!!! Thanks in advanced! Anthony

 

[Faztbullet]

Re: Mercury 115 2+2 questions

Its not the ignition its the carbs, it runs on 2 the jumps to the other 2 . These engines are very picky about the sync & link and if off it will bogg and have hole shot problems.

 

[sschefer]

Re: Mercury 115 2+2 questions

hey guys and gals,
I just completed my full rebuild on my 1990 115. I know it has a 2+2 ignition setup, is there more info on tricking the factory ignition? I haven't even gotten past the 2 hour mark, but I can tell it doesn't have that much balls down low. It is on a 19' fish and ski, and it will be used more for ski than fish.......So I need all the hole shot I can get!!! Thanks in advanced! Anthony

Faztbullet is right about the 2+2. It came in two flavors 100 and 115. Both are troublesome to setup but once done can perform decently. Don't expect a lot of top end out that 19' boat. The way they work is that there is insufficient fuel in the mix on 3 and 4 to support combustion below 1800 rpm but it is adequate to support lubrication. When you begin to accellerate the mixture become adequate to combust and the engine begins to run on all 4. The carbs are tuned for their specific cylinder so if you ever rebuild them don't swap them around..

A decent hole shot can be had with these engines but you need a vented prop and you need to just flat out stuff it so the accelerator pump squirts a lot of extra fuel into 3 and 4. 3 and 4 have injectors in addition to the carbs.

If you need a spare I have one in my shop that is just sitting. I also have a spare set of carbs and a attenuator plate if you ever need them.

 

[ohmthis]

Re: Mercury 115 2+2 questions

Thanks guys, I'll keep the spare parts in mind!

 

[CharlieB]

Re: Mercury 115 2+2 questions

Spare set of carbs????????

PM me.

 

[sschefer]

Re: Mercury 115 2+2 questions

Spare set of carbs????????

PM me.

Done..

 

[twopunches]

Re: Mercury 115 2+2 questions

i also have a set of carbs off 1992 115 2+2
a stator and switchbox and trigger assemblyand a nice tilt and trim
also have rebuilt fuel pump blew my motor kept all eletronics
carbs newly power tuned

 

[Texasmark]

Re: Mercury 115 2+2 questions

Its not the ignition its the carbs, it runs on 2 the jumps to the other 2 . These engines are very picky about the sync & link and if off it will bogg and have hole shot problems.

Hey Faz, would you elaborate more on that 2+2 setup. I thought they just killed one of the pair of triggers to the pulse paks to kill 2 cyls, but that was just a WAG. One of the things I wondered about was what the cylinders thought about being shut down at low speeds and then being asked to put out full power when told to do so....seemed risky to me.

So now I hear that they do it with carb sink and that they alternate cylinders that are loafing!

I bought a 3 banger and stayed off the 4's because I was afraid of this system.....personally would rather have had all 4 operating 100% of the time.

Thanks,

Mark

 

[CharlieB]

Re: Mercury 115 2+2 questions

The 2 + 2 system is ALL in the carbs, the ignition aside from being a 4 cyl, functions exactly like that of the 3 cyl modules.

The top two carbs are normal in form and function.

The difference is the bottom two carbs DO NOT have a pilot circuit drilled and DO NOT begin to pass ANY fuel until the throttle is open far enough that suffient air flow begins to pull fuel.

Thus, the engine idles on only the top two cyl's.

To aid in acceleration an accelerator pump is installed and plumbed into only the bottom two carbs, adjustment is critical to enrichen the air flow when the throttle is first opened.

This system works well on lighter boats that are used for tubing and skiing as a rapid throttle opening accelerates briskly, most operators will never notice any transisition, nor that the idle was only on 2 cyl's.

Heavier boats used for fishing, trolling above an idle, often operators keep readjusting the trottle in attempt to get their trolling speed just right.

Thanks to sschefer, I am replacing my bottom carbs and removing the accel pump, changing my 2 + 2 into a full time 4. Will see how well it trolls when the weather warms up, it's freezing right now.

 

[Texasmark]

Re: Mercury 115 2+2 questions

Thanks to sschefer, I am replacing my bottom carbs and removing the accel pump, changing my 2 + 2 into a full time 4. Will see how well it trolls when the weather warms up, it's freezing right now.

Well I'll be............ Heck, if I'd have known that's all it took I would have certainly been out after a 4 banger.

Thanks,

Mark

 

[swordfish25]

Re: Mercury 115 2+2 questions

My son has a 115 2+2,[might be in the mid to lato 90s] and it keeps dropping a cylinder around 3000 rpm. Changed pluges and no change. Seems like one cylinder keeps cutting in and out . Seems ok at full throttle. People have worked on it and say that is how they run. I can`t seem to buy it. Any ideas?

 

[backyard mechanic]

Re: Mercury 115 2+2 questions

The difference is the bottom two carbs DO NOT have a pilot circuit drilled and DO NOT begin to pass ANY fuel until the throttle is open far enough that suffient air flow begins to pull fuel.

Thus, the engine idles on only the top two cyl's.

So how do they lubricate the cylinders so they don't score at low speed??? Interesting! .... No wonder they changed to full time 4 cylinder operation!

 

[sschefer]

Re: Mercury 115 2+2 questions

Well I'll be............ Heck, if I'd have known that's all it took I would have certainly been out after a 4 banger.

Thanks,

Mark

This trick works to make it more like a full time four.

Pull the pulse fuel pump off them and run a 5-7lb electric and it will act darn near like a full time 4. The injectors on 3 and 4 only need 5 lbs to open. The accelerator pump is there to smooth the transition while the fuel pump builds enough pressure (about 1800 rpms) If you're running the oil pump change it over to a inline versus pump top check valve or just remove the oil injection and run pre-mix.

 

[Faztbullet]

Re: Mercury 115 2+2 questions

The carbs used on cylinders number 3 & 4 are the difference, the off idle discharge ports are located futher from the intake so the fuel/air mixture at idle speeds is too lean for combustion to occur, yet enough to lube the cylinders. When engine reaches around 1800 rpm, air flow through carbs increases and the fuel/air mix to cylinders 3 & 4 is sufficient to support
combustion and all four cylinders become operational. The throttle linkage operates the accelerator pump which provides extra fuel to cyls 3 & 4 during rapid acceleration. Fuel from the accelerator pump goes through a inline filter and then to the injectors located on the transfer port of cylinders 3 and 4. The injectors are equipped with check valves that unseat
at approximately 11-14 psi allowing fuel to flow into cylinders.

Pull the pulse fuel pump off them and run a 5-7lb electric and it will act darn near like a full time 4. The injectors on 3 and 4 only need 5 lbs to open.

Who told ya that Steve??? If you did that and injectors where to open, it would flood cylinders as no way to control amount of fuel introduced by pump

 

[Texasmark]

Re: Mercury 115 2+2 questions

Thanks for the discussion guys.

Mark

 

[pigeon laker]

Re: Mercury 115 2+2 questions

The injector nozzles are for the fuel bleed system.Follow the small hoses and you will see that all cylinders are connected together in this system.If any of the check valves(there are 4)are not operating correctly or if any of the nozzles are plugged the fuel will pool in the cylinders causing flooding and poor performance.

 

[sschefer]

Re: Mercury 115 2+2 questions

The carbs used on cylinders number 3 & 4 are the difference, the off idle discharge ports are located futher from the intake so the fuel/air mixture at idle speeds is too lean for combustion to occur, yet enough to lube the cylinders. When engine reaches around 1800 rpm, air flow through carbs increases and the fuel/air mix to cylinders 3 & 4 is sufficient to support
combustion and all four cylinders become operational. The throttle linkage operates the accelerator pump which provides extra fuel to cyls 3 & 4 during rapid acceleration. Fuel from the accelerator pump goes through a inline filter and then to the injectors located on the transfer port of cylinders 3 and 4. The injectors are equipped with check valves that unseat
at approximately 11-14 psi allowing fuel to flow into cylinders.

Who told ya that Steve??? If you did that and injectors where to open, it would flood cylinders as no way to control amount of fuel introduced by pump

I read the book, tested my injectors and just did it. It worked fine. The injectors unseat a lot sooner than 11-14, it's more like about 5-7lbs on brand new ones. I set the fuel pump pressure regulator to 4-5 lbs and it worked perfect.

You remember all the probs I had with my 2+2 but I finally got it all dialed in. The best it ever ran was on pre-mix with the Holley Red fuel pump.

The guy that has it now say's he loves it and he's running it setup just like I did. It's in Miami getting a winter tan now.

 

[Faztbullet]

Re: Mercury 115 2+2 questions

I read the book too and post is from service manual....did you still use the accelerator pump?

 

[sschefer]

Re: Mercury 115 2+2 questions

I read the book too and post is from service manual....did you still use the accelerator pump?

Yep, I recognized it word for word. Good to hear somebody else knows what the manuals are for.

I tried it both with and without the accelerator pump. It lagged badly without it so I put it back on. The pump doesn't add any pressure it just controls volume unless your pumping the throttle I guess.

I don't know where they came up with that 11-14 lbs of pressure. They have 3/8 inlet and outlets instead of the normal 5/16 but other than that they are the same as any other pulse pump. I put my pressure gauge on it and watched and it got close to 6 lbs at WOT but never any 11-14. I also talked to a couple of other Merc Mech's about that number. They just looked at me like I was nuts.

I gave the manual to the guy who bought it but I think I remember the injector test being 5-7. Less than 5 means a bad spring and more probably means they need cleaning. My originals were still at 9 after cleaning so I replaced them. The new ones opened at 7 right out of the package. The spec's are in the book so correct me if I'm wrong on the numbers. I know I never had a problem with them after that.

The problem I was chasing with my 2+2 ended up being one stinkin coil that was cracked and double firing. Looked good in all the book tests but the final test was just to replace them all. That cured it.

 

[sschefer]

Re: Mercury 115 2+2 questions

The difference is the bottom two carbs DO NOT have a pilot circuit drilled and DO NOT begin to pass ANY fuel until the throttle is open far enough that suffient air flow begins to pull fuel.

Thus, the engine idles on only the top two cyl's.

So how do they lubricate the cylinders so they don't score at low speed??? Interesting! .... No wonder they changed to full time 4 cylinder operation!

Actually, the bottom two carbs do deliver fuel at all times just not a rich enough fuel/air ratio to support combustion. These engines also do not have typical sealing rings on the crankshaft so the excess oil from 1 and 2 runs down to 3 and 4 to help with lubrication.