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1999 125 1.9 litre, 125422vd, second pair of cylinders not firing

C

ChainBender

New member
this motor is new to me so I'm lost. Bass Pro in Destin, FL took it off and put it on a pallet for the man I bought it from. He said he used it the day before it was removed and ran great.

I had it mounted and all new wring from console back to motor put on it. Carburetors cleaned, New battery cables and new shift/throttle linkage professionally installed and adjusted.

I put new plugs, ECM's on it also. Compression is 140# on all 4 cylinders.

As I understand it, the engine idles on 2 cylinders and the other two kick in when the engine is shifted into gear. Engine is mounted on a 1987 Aluminum boat hat was rated for 120 HP back then. Engine has a 17 pitch prop on it. Runs really rough and shutters bad during acceleration. Engine will only come up to 4600 rpms and will only push this light boat at 33 mph.

was told by a professional mechanic that it has 2 stators. One for each pair of cylinders. Crowley Marine only shows one.

Any way I need help. Any assistance will be greatly appreciated.

ChainBender
 
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1 stator, 4 CDMs,engine transfers from 2 to 4 cylinders in the 1800-2200 RPM range, not when shifting into gear. Sounds like fuel system needs attention, carbs ,fuel pump diaphragm, accelerator pump, and fuel lines for degrading internally....
 
The 2+2 motors idle and run on the top 2 cylinders up to 1800 rpm. The the bottom 2 cylinders kick in after that. There is no idle circuit in the bottom 2 carbs and there is not 2 stators. The early ones had high and low speed windings in the stator and later ones don't. You may be a little over propped because the operating range is 4750-5250 rpm. You may also need to do a link and sync and the Factory service manual is a MUST for that motor. The link and sync is critical on those motors and only the factory manual can guide you through it.
 
flyingscott said:
The 2+2 motors idle and run on the top 2 cylinders up to 1800 rpm. The the bottom 2 cylinders kick in after that. There is no idle circuit in the bottom 2 carbs and there is not 2 stators. The early ones had high and low speed windings in the stator and later ones don't. You may be a little over propped because the operating range is 4750-5250 rpm. You may also need to do a link and sync and the Factory service manual is a MUST for that motor. The link and sync is critical on those motors and only the factory manual can guide you through it.
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totally disagree on being over propped. I had a 4 blade 21 pitch and a 23 pitch prop on it and still got the same performance. The boat with gas and battery probably don't weigh 1000 pounds.

Something must be wrong with what ever regulates the firing. at idle I can pull the top two plug wires off and there is absolutely no change in the idle. but if I pull either of the bottom to plugs the engine dies immediately. Maintenance records from July 2016 show most of the gas problems mentioned above were taken care f ten. Even the fuel pump was rebuilt. Every time take the boat out for a test run and come back to the landing the top two plugs are soaking wet.

Guess I'm gonna have to take it to a shop then. All the remedies mentioned above are beyond my skills.

thanks for the replies,
ChainBender
 
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Sounds like somebody put.the carbs on wrong cylinders. Or the fuel system is plummed wrong or needs serious attention. That motor will always have spark on all 4 cylinders. And it should never idle on the bottom 2 cylinders at all. Time to look at the fuel system. I would also take a look at your tach because it is doubtful a 4 blade 21 or 23 pitch would run the same as a 17 pitch 3 blade. Find somebody who knows about the 2+2 motors.
 
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flyingscott said:
Sounds like somebody put.the carbs on wrong cylinders. Or the fuel system is plummed wrong That motor will always have spark on all 4 cylinders. And it should never idle on the bottom 2 cylinders at all.
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If it was running fine when it was taken off his boat and put on a pallet it was running fine. Admittedly, I did sit in my barn for several months before I mounted it on the boat and took it to a shop to have a new control box and cables put on, new battery cables, and new ignition switch put on. Also the wiring harness that plugs into the motor is brad new. It ran bad on the first run runS an then I had the carbs cleaned. Didn't notice one bit f improvement in performance.

I know I'm giving negative answers here, but I'm doing my best to explain what I'm seeing and doing while I'm unplugging wires and taking out plugs.

tks again.
 
Ok It is almost a physical impossibility for your motor to run on the bottom 2 cylinders at an idle. That is because there are NO idle circuits in those 2 carbs which means no fuel. They bottom cylinders can fire and make the motor run rough if the accelerator pump on them leaks. But the motor would still be running on the top 2 cylinders and since it doesn't you have an issue. Find a GOOD mechanic who knows about the 2+2 motors. Who said it was running fine? Did you see this motor running fine? Find a good Mechanic, you notice I said that twice right.
 
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flyingscott said:
Ok It is almost a physical impossibility for your motor to run on the bottom 2 cylinders at an idle. That is because there are NO idle circuits in those 2 carbs which means no fuel. They bottom cylinders can fire and make the motor run rough if the accelerator pump on them leaks. But the motor would still be running on the top 2 cylinders and since it doesn't you have an issue. Find a GOOD mechanic who knows about the 2+2 motors. Who said it was running fine? Did you see this motor running fine? Find a good Mechanic, you notice I said that twice right.
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the owner I bought it from and the mechanic who put all the new wires and cables on it aid it was running fine. Although the mechanic only ran it on a hose. I'll try to make a short video of it running on a hose tmw and post it. Thanks to all, CB

And I have read that the two non firing cylinders still get a minute amount of fuel to provide lubrication.
 
Yes They only get enough for lube but they wont fire. You need a good mechanic who knows how to work on the 2+2 motors. They are not the easiest to work on and a lot of guys hate them. That is the 3rd time about the mechanic.
 
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I have twin 2+2 115's on my Aquasport and have done all the work on them since new in 1995 and have an excellent understanding of how they operate. The engine should not be running on the bottom 2 cylinders at idle. Take the cowling off and look at the bottom carbs from the port side and see if there are idle mixture adjustment screws in the upper rear of the carbs. This would suppprt the fact that the wrongs carbs were installed on the bottom cylinders. As stated, the engine is designed to get enough lubrication at idle but not enough to fire the cylinders.
 
fitz73222 said:
I have twin 2+2 115's on my Aquasport and have done all the work on them since new in 1995 and have an excellent understanding of how they operate. The engine should not be running on the bottom 2 cylinders at idle. Take the cowling off and look at the bottom carbs from the port side and see if there are idle mixture adjustment screws in the upper rear of the carbs. This would suppprt the fact that the wrongs carbs were installed on the bottom cylinders. As stated, the engine is designed to get enough lubrication at idle but not enough to fire the cylinders.
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Well, I know you AIN'T gonna believe me, but all 4 carbs have mixture screws! I would post a pic but I guess I don't have that privilege yet. gonna be even harder to post a video of it running with the top two plug wires pulled??
 
Here is what is possibly happening somebody tried to eliminate the 2+2 operation and it does not work. You may need to buy a bottom set of carbs to put it right. Hopefully all the parts are there yet for the accelerator pump assembly. I would also make sure you have 125 carbs on there.
 
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I'm thinking I', just gonna replace this one with a good used 90-140 something. I spent almost $1400 parts and labor to have this thing hooks up and cranked. can replace it for a couple of thousand.

thanks to all for your inputs. They were all much appreciated.

Chain Bender
 
I've heard of it being done but this is first one I've seen converted. The story behind the 2+2 was the engine would not idle correctly if all four cylinders were fed fuel at idle so the engine was re-engineered to the 2+2 configuration. There must have been a lot more to the story for Mercury to go through the expense of doing it.
 
I did some testing this morning at idle, 2000, 2400 and 3000. Not only are the idle carbs as backwards, the 1800 rpms second pair of cylinders doesn't come in until 2400 rpm but s you can see in the 4th vide at 000 rpms, the top two cylinders have definitely come it an running strong at 3000, but now the lower pair of cylinders have gone out. At no time is this motor running on all 4 cylinders. According to the book and to every thing you guys have said, THIS ENGINE IS RUNNINN ASS BACKWARDS TO WHAT IT SHOULD BE RUNNING AND IT SWITCHES PAIR(s) OF CYLINDERS WHEN ALL 4 SHOULD BE RUNNING. Does this sound abut right?


I'VE TRIED ALL MORNING TO POST VIDEOS TO YOU UBE AND ATTACH THE LIKS WITHOUT SUCCES. SORRY !!!
 
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Yes, totally ass backwards. Regardless of throttle position all 4 cylinders fire the sparkplugs all the time. The difference is the bottom two are not fueled below 1800 rpm and are just along for the ride (with the sparkplugs firing but no fuel). When you hit 1800+ rpms the engine starts to draw fuel through the high speed jet and runs normally. It simply a matter the engine creating enough vacuum through the carb venturi to pull the fuel on those two cylinders. It is not any complex cylinder deactivation like on today's automobile or truck engines. That said, the only thing that determines which cylinders fire at the right time is the trigger coil (under the flywheel) which tells the coil/amplifier packs to discharge voltage and fire the plug at the correct time. To me, that is the only common denominator between all 4 cylinders. It may be worth it to get the trigger coil tested to see if it could be the culprit.
 
Is it possible that the new wiring harness from the binnacle back to the starter, tach,.... could be t wrong year/model/make? I just spoke with the gentleman I the motor from and he said he never had an issue with it.
 
No, pretty much plug and play. Same harness used on carburetor models for 30 years. The harness has nothing to do with the engine running. The engine will run with the harness unplugged. Harness is needed to turn starter, shut off engine, run gauges. Charging is done through the battery cables.
 
Stop doing what you are doing you have no understanding at all of how that motor works. At the very least get the correct manual for it. In neutral that second pair of cylinder will not be running at 1800 rpm. The 2+2 operation is load dependent. Which means you need to be in gear and in the water for it to work. You could rev that motor to 5000 rpm and it would stay on 2 cylinders in neutral. Get a good mechanic to look at your motor.
 
Finally someone who can explain exactly how this engine works, please explain because honestly I've never met anyone who can. I've owned a pair of these since 1995 and no one except myself as ever turned a wrench on them and they still run perfect. They are odd critters. I certainly invite your insight into this design and look forward to the discussion.
 
OK here is how the 2+2 motor works it's pretty simple and elegant. The motor idles and starts on the top 2 carbs those have primers for starting. The bottom 2 carbs have no idle circuits that's why they have the accelerator pump. All 4 cylinders always have spark that is important to know. When you first start it and are running on the lake below 1800 rpm you are running on the top 2 cylinders. While that is happening the bottom 2 carbs are providing a minute amount of fuel mix to keep everything lubed but not enough to run. As you accelerate the 2 top cylinders are fine but now it is time for the bottom 2 to come in. That is where the accelerator pump comes in since the bottom 2 carbs have been providing no fuel. The accelerator pump injects a fuel mix into the cylinder to jump start them until the carb takes over. If the accelerator pump was not there there would be a huge lag in the acceleration of the motor. Now it is running on 4 when you throttle down the opposite happens. If you want to know about accelerator pumps ask a guy who has had or remembers when cars had carbs on them. And that is why you cannot test the 2+2 operation in neutral. 1800-2000 rpm in neutral has a very different throttle position than 1800-2000 rpm in gear.
 
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