Re: how to bypass Mariner 115HP 2+2 cylinder activation
I've been reading your threads, and I can tell you that I had the same questions when I first bought my Mercury 115 (brand new) way back in 1997. It took me forever to find a mechanic who could actually explain how the setup worked, and I just couldn't believe that Mercury would come up with such a surprising design. I had actually ordered the official Mercury maintenance manual to try and find an explanation, but not one word on this design peculiarity! I'm sure nobody at Mercury wanted to take ownership of such a strange invention!
Having said that, my outboard now has over a 1,000 hours of operation, and works (and has always worked) like an absolute top. Mostly high-speed water-skiing, but also a fair amount of slow operation. I finally found somebody moderately competent who told me that indeed, only the top two carbs have an idle jet, but then he couldn't explain how the lower two cylinders didnt's seize up on idle for lack of lubrication. Thanks to this thread, I now have the explanation. It's because the lower two cylinders manage to draw just enough fuel through the main jets to keep the thing sufficiently lubed.
The one thing this guy couldn't explain to me was the purpose of a plastic tubing that runs the full length of the engine block, and branches off into the bases all all four cylinders through little check valves. I don't have a clue what this tube is for. And there again, the stupid official manual shows this on a drawing, but doesn't say one word about its purpose. The loose end of this tubing seems to end up in carburetor N? 1. Anybody have an idea what it's for? That would solve the last mystery of my beloved 115, which has now served a full 15 seasons!
I want to add that I never ever gave this motor in for service. I did absolutely all the maintenance myself ever since I bought it, and it never failed me. Would you believe that the water pump impeller is still the original one (and the pee hole discharges a great and steady flow without any overheating problem), and the thermostat also? And this is a boat that I use for a full month each year in salt water! I rinse it carefully at the end of the season, and perform the normal cylinder oiling, bracket greasing and all the standard checking stuff. But to date, there are no signs of wear or faulty operation. The engine starts at first kick every new season. I change the plugs every second year, and clean and regap them every intermediate year.
One last thing about this strange 2+2 setup: I have to admit that the fuel consumption of this motor is noticeably lower than equivalent motors of that time. We had many occasions to compare with a friend with whom we go boating. His is powered by a Yamaha 115 hp V-4. Nice engine, smooth, but it drinks gas like heck compared to my Mercury. By the way, whatever the manual says, don't use any ethanol-mixed gas. It's crap, and I know loads of people who have had problems. Pay a bit more for fuel, and be safe.
Oh! When I say this engine never failed me: small problem, big consequences. For a couple of years, once or twice during the season, the thing just stopped dead, sometimes with a short squeal from the alarm horn. After fiddling with the starter, it would usually resume operation. Elusive electrical malfunctions are the most difficult to find, and I saw nothing amiss. Last season, it had the good taste to stall completely and to refuse any further service, so at least this time I could really look for what caused the ailment. It was actually just the wiring harness grounds (there are several) that had slightly loosened over the years. The protective oil had probably gotten to the threads, and actually cut off the ground, causing a total loss of ignition. A quick tightening of all the wiring harnesses, and the problem was gone! Before you let any mechanic tell you that there is some expensive electronic gizmo that needs replacement, just think of checking this before spending any money.
I've been reading your threads, and I can tell you that I had the same questions when I first bought my Mercury 115 (brand new) way back in 1997. It took me forever to find a mechanic who could actually explain how the setup worked, and I just couldn't believe that Mercury would come up with such a surprising design. I had actually ordered the official Mercury maintenance manual to try and find an explanation, but not one word on this design peculiarity! I'm sure nobody at Mercury wanted to take ownership of such a strange invention!
Having said that, my outboard now has over a 1,000 hours of operation, and works (and has always worked) like an absolute top. Mostly high-speed water-skiing, but also a fair amount of slow operation. I finally found somebody moderately competent who told me that indeed, only the top two carbs have an idle jet, but then he couldn't explain how the lower two cylinders didnt's seize up on idle for lack of lubrication. Thanks to this thread, I now have the explanation. It's because the lower two cylinders manage to draw just enough fuel through the main jets to keep the thing sufficiently lubed.
The one thing this guy couldn't explain to me was the purpose of a plastic tubing that runs the full length of the engine block, and branches off into the bases all all four cylinders through little check valves. I don't have a clue what this tube is for. And there again, the stupid official manual shows this on a drawing, but doesn't say one word about its purpose. The loose end of this tubing seems to end up in carburetor N? 1. Anybody have an idea what it's for? That would solve the last mystery of my beloved 115, which has now served a full 15 seasons!
I want to add that I never ever gave this motor in for service. I did absolutely all the maintenance myself ever since I bought it, and it never failed me. Would you believe that the water pump impeller is still the original one (and the pee hole discharges a great and steady flow without any overheating problem), and the thermostat also? And this is a boat that I use for a full month each year in salt water! I rinse it carefully at the end of the season, and perform the normal cylinder oiling, bracket greasing and all the standard checking stuff. But to date, there are no signs of wear or faulty operation. The engine starts at first kick every new season. I change the plugs every second year, and clean and regap them every intermediate year.
One last thing about this strange 2+2 setup: I have to admit that the fuel consumption of this motor is noticeably lower than equivalent motors of that time. We had many occasions to compare with a friend with whom we go boating. His is powered by a Yamaha 115 hp V-4. Nice engine, smooth, but it drinks gas like heck compared to my Mercury. By the way, whatever the manual says, don't use any ethanol-mixed gas. It's crap, and I know loads of people who have had problems. Pay a bit more for fuel, and be safe.
Oh! When I say this engine never failed me: small problem, big consequences. For a couple of years, once or twice during the season, the thing just stopped dead, sometimes with a short squeal from the alarm horn. After fiddling with the starter, it would usually resume operation. Elusive electrical malfunctions are the most difficult to find, and I saw nothing amiss. Last season, it had the good taste to stall completely and to refuse any further service, so at least this time I could really look for what caused the ailment. It was actually just the wiring harness grounds (there are several) that had slightly loosened over the years. The protective oil had probably gotten to the threads, and actually cut off the ground, causing a total loss of ignition. A quick tightening of all the wiring harnesses, and the problem was gone! Before you let any mechanic tell you that there is some expensive electronic gizmo that needs replacement, just think of checking this before spending any money.
