Newbie Questions 1990 115 4cyl OB

[made in china]

Hey ya'll, I've searched the forums a bit to get a feel for the motor I have, a 1990 Mercury 115HP 4cyl OB. But, I have a few questions and things I need clarified. I am a 2 stroke OB newbie!

1. Can I pull start this motor if my battery dies? I heard it can be, but in my Merc FSM, I couldn't find the procedure. If it's possible, what do I need?

2. In my research, I found that Merc 115's get about 11.5-14.0 GPH at WOT, but I couldn't determine if the ratings were for the 4cyl or 6cyl. What should my motor consume?

3. Also found out that the motor will run on 2 cylinders at lower speeds, switching to 4 cylinders as the revs come up. I heard that it is inconvenient for wakeboarders, of which I am one. My boat is a 1986 Larson 175 open bow, about 1100 pounds dry (w/o motor or fuel, people). I have a 13 x 21 prop on it. Will I have wakeboarding troubles around the 2-4cyl switchover?

4. From dead cold, how many pumps should I pump the primer bulb?

Thanks guys for any help!

 

[achris]

Re: Newbie Questions 1990 115 4cyl OB

Hey ya'll, I've searched the forums a bit to get a feel for the motor I have, a 1990 Mercury 115HP 4cyl OB. But, I have a few questions and things I need clarified. I am a 2 stroke OB newbie!

1. Can I pull start this motor if my battery dies? I heard it can be, but in my Merc FSM, I couldn't find the procedure. If it's possible, what do I need?

Yes you can pull start your engine. Not fun, but it can be done. The procedure is in your owners manual. All you need to do it is a length of rope with a knot in one end. DON'T wrap the rope around your hand when you do it.

2. In my research, I found that Merc 115's get about 11.5-14.0 GPH at WOT, but I couldn't determine if the ratings were for the 4cyl or 6cyl. What should my motor consume?

Fuel consumption varies a great deal, depending on the weather, the boat loading, the boat trim, and the activity your doing. All that said, your engine should be consuming around 11-14 GPH at WOT.

3. Also found out that the motor will run on 2 cylinders at lower speeds, switching to 4 cylinders as the revs come up. I heard that it is inconvenient for wakeboarders, of which I am one. My boat is a 1986 Larson 175 open bow, about 1100 pounds dry (w/o motor or fuel, people). I have a 13 x 21 prop on it. Will I have wakeboarding troubles around the 2-4cyl switchover?

Depends on the speed you wakeboard at... If you do find you're having problems, talk to the dealer and see if a different prop will help... You may find a nice prop is a Laser II with the vent plugs removed.

4. From dead cold, how many pumps should I pump the primer bulb?

Squeeze the primer until it is firm. Not rock hard, you'll just push the carb needles off their seats and flood the engine.

Chris..........

 

[109jb]

Re: Newbie Questions 1990 115 4cyl OB

I'll have to verify when I get home but I don't think my 4 cyl 115 (1998) has the provision in the flywheel for rope starting.

As for the 2+2 where 2 cylinders are firing at low speed, the other 2 come on very early and I doubt that you will have a problem for wakeboarding. When I got mine it ran like crap. I went through the adjustment procedures in the service manual and all is well now. Basically the way they did the 2+2 is they have 2 carburetors installed that don't have idle circuits in them so no fuel gets to those cylinders. It has been done by others and I had considered replacing those 2 carbs with ones like the other 2 that have idle circuits. That would eliminate the whole only running on 2 thing. Too expensive to do this if you buy new carbs, but when I was considering it I found some on e-bay. Out of curiosity I just checked and there is a complete set of carbs from a 1997 115 ELPTO with a buy it now of $197. You would have to check to make sure the 97 115 uses the same carb as yours but that would give you 2 more carbs with idle circuits. After giving mine a good tune up it works fine using the stock 2+2 system for what I do. Here is a link to those carbs on e-bay if you are interested. Remember to check to make sure they are the same as yours if you decide to buy.

 

[made in china]

Re: Newbie Questions 1990 115 4cyl OB

Thanks for the input guys. When I bought this boat, I took the motor cowling off to inspect it, and it seemed that the flywheel could be rope started. But, I wasn't sure. I don't have the owners manual for it.

I took it out for a test drive, and the 2-4cyl thing was fairly apparent. At first I just thought it was the 2 stroke coming "on the pipe", but now I realize it was the 2-4cyl setup. I think the switchover may happen early enough for me. That being said, I am very surprised at how smooth my old OB runs, at idle I can barely notice it running. When I was starting it, it fired up so smoothly and set into a smooth idle I had to check the tach because I expected a 2 stroke OB to be noisier and rougher. And to find out it idles on 2 cylinders is a surprise too!

Maybe I'll keep my eyes open for carbs like 109jb said. I can't see the 2-4cyl setup saving much fuel as it only affects the idle and low speed.

 

[achris]

Re: Newbie Questions 1990 115 4cyl OB

I've done the conversion at customers insistence... You WILL lose that super smooth and quiet idle. When they are on all 4 they are quiet rough... Hard to believe, but true.

Chris......

 

[MercGuy]

Re: Newbie Questions 1990 115 4cyl OB

109jb - I also have a '98 115 and it does have the notches for rope starting. I bought my outboard new in 99, and during that last 11 years I've used this feature twice. The first time it was just a convenience, as I arrived at the ramp with a dead battery but was able to boat that day anyway. The second time I avoided a possible catastrophe. I was on the Ohio River and shut my engine off. When I tried to re-start the battery was dead as a door nail. I guess it had an internal short or a broken plate. So there I was drifting down the Ohio River w/o power. It wasn't obvious to me what the problem was at first since everything on the boat went completely dead. I assumed it was a fuse. I was drifting towards a bridge piling and saw a barge off in the distance. I still thought the problem was a fuse, but didn't have time to screw with it. I took the cowling off, wrapped the factory supplied rope around the flywheel and it started on the first pull. Talk about relief !!!

I think that the rope start feature of old 2 strokes is a major advantage and is one of the reasons that they will have to pry my 2 stroke from my cold dead fingers


achris - you are the first poster that I am aware of that has done the carb conversion. I always wondered how that would turn out. I'm very surprised to hear that it idled poorly, I would have expected the exact opposite. Do you have any other details ?? Did the owner keep the engine that way ?? Did it burn significantly more gas ?? I'd be very interested to know.

 

[sschefer]

Re: Newbie Questions 1990 115 4cyl OB

Drop the pitch down on the prop and you'll be able to sustain a higher rpm at lower speeds for a bigger wake and be running well into the all 4 range.

Trim the motor up to keep the bow up (more wake) and use a vented 4 blade prop for a better hole shot. I ran my 100 2+2 with a 4 blade 14x16p Stilleto Bay Runner. After I was declared insane I started running V-6's.

Do not modify the engine to run on all 4 always. You can do it but you'll be futzing with it forever and like achris say's that smooth idle will be gone.

If you really want to make it run on all 4, at least wait until CharlieB gets his done. I gave him a set of carbs last winter so we might see something soon. If I know him, there will be a detailed explanation on how to do it including what needs to be done with the injectors on #3 and 4# that you don't know about yet.

 

[109jb]

Re: Newbie Questions 1990 115 4cyl OB

109jb - I also have a '98 115 and it does have the notches for rope starting.

Yeah, I looked when i got home this evening and I have them too. I was mistaken.

 

[109jb]

Re: Newbie Questions 1990 115 4cyl OB

The 2+2 setup really does work pretty well if properly tuned. When I got my motor the previous owner had it all screwed up. I just did the step by step from the service manual and it runs very very well. The idle is good and the power is good. Throttle response is also good. When the engine goes from 2 to 4 cylinder operation you can definitely hear and feel it but for most thing it won't matter.

Until I got the service manual with the procedure I futzed with it and got nowhere. That was when I was considering replacing the 2 carbs to make it run on all 4. I did find some information where someone described what they did to get it to run on all 4 cylinders and they reported it ran very well. I'll see if I can find the link but that was 2 years ago.

 

[made in china]

Re: Newbie Questions 1990 115 4cyl OB

So we took it out yesterday and ran the boat for a few hours. It ran great, the 2/4cyl thing isn't so bad, but it may jerk a wakeboarder out of the water a little too quickly. For a beginner, it may be a prob.

One thing I noticed, my boat had a Merc 150, prev owner put this Merc 115 on it. So, the trim and water temp gauges that are on the dash are dead. I researched the trim, seems my type of outboard didn't come with the sensor installed. So, I plan on getting a used QS Voltmeter to replace the trim gauge. However, in my Mercury FSM, there does not seem to be a provision for temp sensor? Only overheat switches? Can I put a temp sender on this motor and get my temp gauge working again? I am kinda OCD about everything working on my boat so I'd like to fix it, any ideas?