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Tan
Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10898
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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I have an 87 force 125 outboard. I have had issues with it,

Customer Question

I have an 87 force 125 outboard. I have had issues with it, got the motor from a friend. First use it ran hot and had a loss of power after running at full speed for 15 minutes. I replaced the impeller, thermostat, cleaned the fuel screen, replaced the bulb on fuel line and the plugs. Not running hot anymore, but when I idle from the boat ramp about 100 yards and then open it up heading out to the islands about 10 minutes away, half way there it chugs for a second then runs at half power but won't run hot. I checked the compression and found as follows. Cyl 1 120, 2-115, 3-111, 4-119..... Help!
Submitted: 2 years ago.
Category: Boat
Expert:  Tan replied 2 years ago.
Hello. My name is ***** ***** I will be assisting you today.
This is most likely loss of spark on one or more cylinders. The way to find out if this is the problem will require a timing light. Run the boat and check the flash of the timing light on each cylinder. The flash must be steady.This test has to be done when the engine is acting up. Now if the engine is running bad now you can check spark with a spark gap tester. The spark should jump a 7/16" gap on the tester. You can use the timing light also for this test while engine is at idle. But if you have no misfire you will have to check spark when it is acting up.
The other things you can try are to choke the engine when it is acting up. Does it run better? The other test is to squeeze the primer bulb. Does it run better?
Do these checks and post back with findings.
Customer: replied 2 years ago.
I do not own a timing light, is this the only way to correctly check it?
Customer: replied 2 years ago.
Also I replaced the plugs today? So wire or coil pack issue? I will try choking it and priming the bulb as well.
Expert:  Tan replied 2 years ago.
Well you could pull each plug wire off the spark plug. The engine will drop rpms drastically if the cylinder is firing. I just don't recommend this hanging over the back of the boat when it is acting up. Believe me it isn't fun as I have had to do this. If you do attempt this procedure be sure you are holding on real good or you might end up in the drink.
The issue could be a coil, cdi module or trigger.
The other way require even more special tools. You can usually rent a timing light at your local auto parts store. I know Auto Zone rents tools.
Customer: replied 2 years ago.
I will rent one from autozone and try that. I will get back with you in a day or so.
Expert:  Tan replied 2 years ago.
Ok , When you do the spark test and find a misfire swap the misfiring cylinder with a known good firing cylinder. If the misfire moves then we know that coil is bad. If the misfire stays then we have another ignition component failing. This will require further testing.
Customer: replied 2 years ago.
Ok ty
Expert:  Tan replied 2 years ago.
Your welcome...................Keep me posted..........Thank you Tan
Customer: replied 2 years ago.
hey tan, i ran the engine on ear muffs and set the timing with a timing light. Also, i popped all wires off while running and had a drop on each one. all acted the same. i did not put the boat in the water and do the timing light test, didn't have anyone to help me so I did it in the yard. if there a way to test for a bad coil or trigger? will they short after running for a few?
Expert:  Tan replied 2 years ago.
If they are sparking now the only test that will show a bad coil is under load test. The trigger isn't as likely to fail. The most common failures on this ignition system is the coil or CDI module. There is an ohm test but it won't show anything with the coil not misfiring. A coil can pass the ohm test and still be bad. So the ultimate test is under load acting up. If you find a coil misfiring then swap it with another cylinder. If the misfire moves the coil is bad. If the misfire stays then the CDI module is bad.
Customer: replied 2 years ago.
also when i remove the number 3 plug wire, it makes a popping sound but not on the other 3 plugs?
Expert:  Tan replied 2 years ago.
That's just the spark from the coil finding a path to ground. Long as the cylinder misfires when plug wire is removed. Now that coil could be cracked and you just can't see it. That would be the suspect coil.
Customer: replied 2 years ago.
gotcha ill keep you updated
Expert:  Tan replied 2 years ago.
Ok choke the engine and squeeze the primer bulb just to be sure it isn't fuel related. If the engine reacts on either of these tests let me know?
Customer: replied 2 years ago.
hey tan, I will be putting the boat in the water in just a few minutes. I cleaned the carbs, replaced the bowl seals and cleaned the fuel filter and blew out all lines as well. Set the timing as well. Gonna put it in the water now, if it chokes down and loses power i will choke it and prime the bulb if it doesn't make a difference what else should i check while its under a loss of power?
Expert:  Tan replied 2 years ago.
Check spark on all cylinders. You can just pull a spark plug wire one at a time the engine should loose rpoms. Use insulated pliers as it will shock.
Customer: replied 2 years ago.
The bulb has full pressure and is hard. When I choke it it stalls. Now it will idle fine and run fine at 3-4 mph. When I throttle up it chokes out
Expert:  Tan replied 2 years ago.
Do you have spark on all cylinders?
Customer: replied 2 years ago.
Pulled number 2 it took the motor about 30 seconds and shut off. Pulled number 1 and it knocked me off the boat but it didn't shut down. Not trying 3 and 4.
Expert:  Tan replied 2 years ago.
Ok I warned you to use insulated pliers. We still need to determine if the other 2 cylinders are firing. If you have just one cylinder not firing it can cause loss of power. Now did you choke the engine when it was coming up on plane? Did you squeeze the primer bulb when coming up on plane? Doing those test with engine not under a load will not reveal a problem. The engine has to be acting up when you perform any of these tests.
Customer: replied 2 years ago.
I did use insulated pliers. They are now in the bottom of lake murray. I did choke it when it came up the plane and the engine stopped. I squeezed the primer bulb in the same scenario and it did nothing.
Expert:  Tan replied 2 years ago.
Ok everything is pointing to an ignition issue. Do you have a timing light?
Customer: replied 2 years ago.
Yes. I checked the timing at full throttle while the engine had no power the timing was showing 32.
Customer: replied 2 years ago.
With the timing light should I see the mark consistently at full throttle? Every few seconds it will disappear and then come back.
Expert:  Tan replied 2 years ago.
Ok we are going to use the timing light to check for spark on all cylinders. Connect the timing light to # ***** cylinder run the boat watch the flash of the timing light. The flash should be steady with no dead spots. Then do the same test on the rest of the cylinders. Now if you find a misfire swap that cylinders coil with a known good firing cylinder. Does the misfire move? If it moves then the coil is bad if it stays we have another ignition component failing which will require further testing with an ohm meter.

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