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1990 Merc 25hp dies trying to get up to full speed

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Rando1971

New member
Here is what I am facing. Motor died last April while running full throttle. First time any issue in 10 years. Found to have no spark. Replaced coils, wires, plugs, stator and power pack. Got it back out and it fired up and did low speed fine. When tried to get it up on plane, it bogs down. If I get off the throttle, it wont die. If I stay on throttle it dies. When accelerating, the bulb feels nice and firm. I did discover I can give it just enough squeeze to get the boat up on plane and have to continue pumping it to keep it running. This does not always work smooth, but it has worked. I have rebuilt the carb, replaced fuel filter, diaphragm, fuel lines, and different fuel tank. No luck. While working my way through these different replacements, the new power pack died. Got another one under warranty and it fired up, but still bogs down. Had it to mechanic as well. All electrical is to spec. He is out of ideas. Been through a lot of forums and still looking for help. Any suggestions are greatly appreciated!
 
Did you buy the complete rebuild kit for the carb. That kit would include fuel pump and primer diaphragm. Did you put the carb base gasket on correctly? Did you use the correct gasket? What is your compression? Did.you soak the carb?
 
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flyingscott said:
Did you buy the complete rebuild kit for the carb. That kit would include fuel pump and primer diaphragm. Did you put the carb base gasket on correctly? Did you use the correct gasket? What is your compression? Did.you soak the carb?
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Thanks all for jumping in with me here.

Yes, used a complete rebuild kit with all the new parts. Even went through the carb a second time to check everything. Carb was soaked and looks excellent-clean and clear. Gaskets looks good. Compression was with specs-think it was 125.

serial #: 0C296789

And diaphragm, with spring and cap is new with carb kit.
 
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Okay, these are a mess. Did you replace both stators, If only replacing one, which one was it? Bigger one, or the small one on the ring? Did you check ohms resistance on trigger (which you did not replace...cheapest part)! If you did check it, did you operate the throttle through full range with ohm meter attached? This will show if you have a bad wire going to your trigger which might interrupt spark signal at certain throttle positions. This is not uncommon, at least here in colder climate. Your symptoms could follow this line of thought.....also could have toasted the box. Or if you didn't replace both stators......could have spiked the box. To tell you the truth, in playing with electronics, I like to change all the components together, that can possibly destroy each other. Final coils, of course are generally good or bad and with a multimeter and visual exam, you can play it safe. So what happened to the box? Got nothing to do with fuel, right? I would get to the root of the problem before you put on that second box, brah!
 
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timguy said:
Okay, these are a mess. Did you replace both stators, If only replacing one, which one was it? Bigger one, or the small one on the ring? Did you check ohms resistance on trigger (which you did not replace...cheapest part)! If you did check it, did you operate the throttle through full range with ohm meter attached? This will show if you have a bad wire going to your trigger which might interrupt spark signal at certain throttle positions. This is not uncommon, at least here in colder climate. Your symptoms could follow this line of thought.....also could have toasted the box. Or if you didn't replace both stators......could have spiked the box. To tell you the truth, in playing with electronics, I like to change all the components together, that can possibly destroy each other. Final coils, of course are generally good or bad and with a multimeter and visual exam, you can play it safe. So what happened to the box? Got nothing to do with fuel, right? I would get to the root of the problem before you put on that second box, brah!
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Only know of one stator ( 86617A20)and a trigger. When first box went out, took to a local mech. He checked electrical and helped get the warranty covered on first box. He ran through all the electric (after everything was installed) and everything was to spec. Does that answer that question correctly?
Second box is on. Have ran it a couple times- trying to play with things to figure something out. That is when I found I could pump the bulb and get it up on plane at times. On coils, they and the wires and plugs are all new and fire seemingly appropriately.
 
Okay, so no charging, no elec start? Is the trigger replaced then too? You didn't mention that in your first post. What is puzzling to me is that why would a fuel problem surface at the same time as an electrical, and why would a new pack suddenly die? I am requesting a confirmation on trigger replacement. If it hasn't been replaced, I would definitely do so. Thanks
 
timguy said:
Okay, so no charging, no elec start? Is the trigger replaced then too? You didn't mention that in your first post. What is puzzling to me is that why would a fuel problem surface at the same time as an electrical, and why would a new pack suddenly die? I am requesting a confirmation on trigger replacement. If it hasn't been replaced, I would definitely do so. Thanks
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Ok, so I am a little confused about the two stator question and the follow up statement about starter. Motor does have electric start. I only see one stator in the diagram. Where is a second stator? Did not replace the trigger. I am not an expert on outboards, obviously, but a decent DIY when I can find the info to follow. So, just trying to keep up with you and trying to see what I missed with second stator...
 
Your charging system has nothing to do with spark on that motor. Did you put the carb base gasket on correctly? Did you use the correct one? Does your spark jump a 7/16" gap? You do not have 2 stators on your motor. You have the ignition pick up and driver coil. Those seldom go bad, if you have no spark have you looked at the kill.switches? The other 2 coils are charging coils. Isyour motor a tiller or remote model?
 
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Hello Mr. Scott. The stator is a 2 piece which includes the charging coil. Without the charging system, it is a 1 piece stator. The question that I had was fielded to determine what exactly was replaced. Do you agree with me to replace the trigger now before we burn out another box? If you want to discuss a fun subject with me lets go to ethanol and Amsoil, my good friend. But first lets get this Merc "runnin' like a song".
 
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timguy said:
Hello Mr. Scott. The stator is a 2 piece which includes the charging coil. Without the charging system, it is a 1 piece stator. The question that I had was fielded to determine what exactly was replaced. Do you agree with me to replace the trigger now before we burn out another box? If you want to discuss a fun subject with me lets go to ethanol and Amsoil, my good friend. But first lets get this Merc "runnin' like a song".
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Post #1 states a mechanic went through the electrical and it was in spec. No I will not debate amsoil with you I dont own stock in the company like you do. The ethanol debate is over.
 
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When you put the base gasket for the carb on did you put it on correctly? Have you tried disconnecting the kill switches. What is the low speed carb screw set at? Is this a tiller or remote model? If a tiller those motors are good for twisting the kill wires and shorting out. The fact you pump the primer and the motor picks up points to a.fuel problem. Is the high idle wire under the flywheel binding?
 
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No I have zero stock in Amsoil, but personally know and spent time fishing with its founder Al Amatuzio. Al introduced us to his products even before they were actively marketed. The man is not only humble, but virtuous. He respected me as a good mechanic and we tested his products with our dirt track and drag strip engines, as well as hundreds of outboard motors. Using dyno results to produce better oils. I have no investment or interest in the company. He wanted me to come and work for him in the late 70's, but my love for my parents, hobbies, and self employment caused me to turn him down. By now I would likely be very high in the company and could afford my own airplane. I am a pilot. I am poor but happy. My dedication to quality, virtuosity, and integrity has kept me away from working for anyone. I replace what I need to make a quality repair and nothing else extra. ALL my repairs and used outboards get a 1 year warrantee........so there, beat that, brother Scott.
Now, the mechanic gave our customer a clean bill of health on the ignition system? Well that's not good enough for me. That trigger is a problematic component, and for 40 bucks it should have been replaced....even if it checked out with the ohmeter.
 
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timguy said:
No I have zero stock in Amsoil, but personally know and spent time fishing with its founder Al Amatuzio. Al introduced us to his products even before they were actively marketed. The man is not only humble, but virtuous. He respected me as a good mechanic and we tested his products with our dirt track and drag strip engines, as well as hundreds of outboard motors. Using dyno results to produce better oils. I have no investment or interest in the company. He wanted me to come and work for him in the late 70's, but my love for my parents, hobbies, and self employment caused me to turn him down. By now I would likely be very high in the company and could afford my own airplane. I am a pilot. I am poor but happy. My dedication to quality, virtuosity, and integrity has kept me away from working for anyone. I replace what I need to make a quality repair and nothing else extra. ALL my repairs and used outboards get a 1 year warrantee........so there, beat that, brother Scott.
Now, the mechanic gave our customer a clean bill of health on the ignition system? Well that's not good enough for me. That trigger is a problematic component, and for 40 bucks it should have been replaced....even if it checked out with the ohmeter.
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Lets get a couple things straight I am not your Brother anywhere or anyhow. #2 I am most definitely not your friend. #2 I dont give a crap about amsoil. It is not a mechanic in a can nor is it the saving grace of any motor. #3 To the Op sorry about this but I am out. Between the sermonizing, Eulogizing ang general baffling with BS this has become painful. Good luck with your motor I am am sure if you throw enough parts at it you can get it to work.
 
Sorry to hear that, Mr. Scott. I am just trying to help this guy fix his motor and I really don't deserve the negative input from you as well as having to defend almost every suggestion I make on this forum. I am far from perfect and do make mistakes myself, obviously one of which is trying to make friends with you.
 
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This is Rando1971’s son. I’ve been the one doing most of the work on the motor, so hopefully I’ll be able to answer everyone’s questions.

I am pretty much convinced the electrical system is good. The motor did completely lose spark on both cylinders, but the new power pack fixed that. After the power pack was replaced the motor refused to run past half throttle when under load. I replaced the stator (just the stator, not the charging coil that’s with it) because I originally checked the wrong wires when I wash checking resistance on the ignition components. I didn’t realize my mistake until after I pulled the flywheel to install the new stator. I rechecked the original stator, new stator, and trigger at this point and everything was within spec. I also checked for continuity on both kill switches and they were good. I inspected and cleaned all the electrical connections in the ignition/charging system before putting everything back together. The other mechanic we took the motor to rechecked everything as well and agreed that it was all good.

The fact act that the motor will stay running after half throttle as long as someone is pumping the primer bulb makes me think it has to be a fuel issue. What has me stumped is that at this point almost the entire fuel system has been replaced. I made sure the carb base gasket was correct and installed correctly. I pulled all the plates, reed valves, etc. between the carb and engine block and replaced all the baskets and seals to try to rule out a vacuum leak. The carb has been completely rebuilt with an OEM kit, the fuel lines and fuel filter on the motor have been replaced, the fuel line on the tank has been replaced, and we tried a different tank.

The only things I see that could possibly be a problem are the fuel line quick connect fitting and the platinum plate on the fuel pump side of the carb. The plastic plate has some minor oxidation and surface cracking due to age. Would that be enough to make the diaphragm not seal properly? I have checked the fuel line fitting for leaks and couldn’t find any, but I guess some kind of obstruction might be possible. Sorry about writing a novel, but hopefully this is enough information to narrow down what the problem could be.
 
Thanks, my bedtime is here so I will write in the morning. -30 here.....actual temp. Brrrr! Just filled both wood stoves for the night.
 
racerone said:
Yesy run with a different tank and hose.
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Not sure what this means, but to clarify: Yes, I did borrow another tank and ran the motor. Did the same thing. Could get power as long as pumped gas bulb. Bulb is firm, takes just a little extra squeeze to boost the power.
 
Well, that means your fuel pump on the motor is not working properly.------Possibly due to issues with crankcase compression.-----Time to trouble shoot fuel delivery issues on your motor.
 
Not really. If it has adequate cylinder compression and no leaks in crankcase, one can assume it is okay. Fuel pumps operate off the crankcase pulses. Is the float level properly set. Maybe at high speed it can't get enough past the needle and seat, but by creating a higher pressure with the squeeze bulb, you can force enough fuel to get it to top speed. You can remove the carb and check that again. Have to make sure the float is dropping down far enough to let open the needle too. Is it hitting something when the bowl is in place?
 
timguy said:
Not really. If it has adequate cylinder compression and no leaks in crankcase, one can assume it is okay. Fuel pumps operate off the crankcase pulses. Is the float level properly set. Maybe at high speed it can't get enough past the needle and seat, but by creating a higher pressure with the squeeze bulb, you can force enough fuel to get it to top speed. You can remove the carb and check that again. Have to make sure the float is dropping down far enough to let open the needle too. Is it hitting something when the bowl is in place?
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Thanks for input. Don't know when I will get the time to tear back into it and then get it back on the water for a test run, but hopefully soon, and I will post an update. It was all free and clear when I was in it before. What could be causing this problem to occur?
 
It has to be a fuel restriction or weakness in the fuel pump. How far below the level of the fuel pump is the gas can? Most pumps will be only able to lift a few feet vertically before dropping in delivery and pressure. I test all mine at about 3 feet of lift. It acts the same using 2 different sets of hose, bulb, and tank?
 
timguy said:
It has to be a fuel restriction or weakness in the fuel pump. How far below the level of the fuel pump is the gas can? Most pumps will be only able to lift a few feet vertically before dropping in delivery and pressure. I test all mine at about 3 feet of lift. It acts the same using 2 different sets of hose, bulb, and tank?
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Its an aluminum duck boat. Fuel tank sits right under the motor in the back of the boat. Less than 2 feet elevation. Yes, it acted the same with two completely different tanks/hose/bulb. This was never a problem before the initial power failure. Since fixing the power, the problem popped up. Crazy!! and frustrating...
 
Sure is....got a gremlin in there? If you don't pressure pump it, does it die a slow death, or wind down?
 
timguy said:
Sure is....got a gremlin in there? If you don't pressure pump it, does it die a slow death, or wind down?
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When goes to die, and I dont pump the bulb, there are two possible results depending on my response:
1. keep the throttle up=the motors dies quickly
2. throttle down= usually will sputter a little but will catch itself and not completely die.
 
This may not be a help, but here is a some insight from my experience. I have a '85 - 60hp 2 stroke. It was dripping gas at the motor from the gas line quick connect after I disconnected the the tank fuel line.

I went out on e-bay and purchased a aftermarket replacement check valve/quick connect fitting.

The aftermarket fitting went in smoothly appeared to worked well, eliminated the drip I was trying to correct, my thoughts great.

Went to the lake, boat started fine, throttled up fine, and then after a short time the motor appeared to starve and die.

If I throttled back it would continue to run just fine at about 1/2 throttle.

I had just thoroughly cleaned the carbs and the motor had run fine prior to changing the quick connect fitting.

The aftermarket fitting was plastic, the original oem fitting was metal, they looked the same, the fuel line connected properly.
Pumping the bulb didn't help. But it was the only think I had changed.

I finally stopped by the marina and purchased the oem parts at four time the price of the aftermarket fitting.

The motor has run fine ever since.

My conclusion was that there was some restriction in the aftermarket part that was not there in the oem version
or the aftermarket part was not the perfect replacement for my particular motor model even though it looked the same from the outside.

Think, what have you changed?
 
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