Trouble Diagnosing Outboard Motor Issue (Video linked)

CMG1039

Cadet
Joined
Apr 21, 2017
Messages
8
Hi,

Looking for any and all ideas as to what may be wrong with my motor.

I have a 1995 Johnson 70 hp, 3 cyl, 2-stroke outboard motor. The motor currently starts and idles fine. I can give it a little throttle and get the boat moving at low speeds. The problem is when I go to give it full throttle. When I do, the motor almost seems like it is limiting out (see video linked below on YouTube). I am only able to go 1/3 of my max speed at full throttle.

Is this an electrical issue like coil packs or stator? Or does this seem to be something like a clogged intake fuel jet? Any ideas on where I should start would be greatly appreciated! Thanks.

https://www.youtube.com/watch?v=rQlFfc_rOU0 <---Link to video of my actual motor issue.
 

CMG1039

Cadet
Joined
Apr 21, 2017
Messages
8
Hi Flyingscott, thank you....a little background. I did have a blown head gasket prior this issue. I changed the head gasket and even had the cylinder head machined down about 2mm to make sure i did not have any warping and a flat surface. Re-installed cylinder head and did compression checks, all three cylinders came back within spec.

I have not done a spark test yet. I will do that tomorrow. If I do have bad spark, what would be the cause?
 

Watermann

Starmada Splash of the Year 2014
Joined
Jan 12, 2013
Messages
13,747
Video was only 6 sec long, not enough time to tell much of anything other than it sounded like it was running only on 2 cylinders. If the compression checks out good and there's spark, when was the last time you rebuilt the fuel pump and cleaned the carbs?

It won't hurt anything to rev the motor a couple k rpms when in the water, it's on muffs that it's a problem due to lack of water flow.
 

CMG1039

Cadet
Joined
Apr 21, 2017
Messages
8
Hi Watermann, I cleaned the carbs (or so i thought), replaced the floats and gaskets at the same time that I changed the head gasket. Could a float be stuck or inlet jet clogged? I thought when its one of those issues the motor usually bogs. This isnt bogging, but more so like it is rev limiting.
 

flyingscott

Fleet Admiral
Joined
Apr 8, 2014
Messages
7,985
I wouldn't rev it neutral with a mis-fire like that things could break. Revving it on muffs isn't bad because of water flow it's because the motor runs lean with no exhaust back pressure on it. Bad spark can be caused by a coil,spark plugs,spark plug wires,CDI Box or timer base or stator. You will need to do some investigating.
 

CMG1039

Cadet
Joined
Apr 21, 2017
Messages
8
Also, I have never rebuilt the fuel pump in the 5 years I have had the motor.
 

Vic.S

Rear Admiral
Joined
May 4, 2004
Messages
4,690
Also, I have never rebuilt the fuel pump in the 5 years I have had the motor.
I am with Waterman. It sounds, and looks, like it is only running on two cylinders.

Do a spark test and also a cylinder drop test as this will identify which cylinder is not firing if one is not.
Swapping plugs between cylinders may identify a bad plug.

Swapping ignition coils will confirm a bad coil if the spark test suggests that may be the trouble.


Do these simple checks before tearing into the fuel pump or the carbs
 

Watermann

Starmada Splash of the Year 2014
Joined
Jan 12, 2013
Messages
13,747
I wouldn't rev it neutral with a mis-fire like that things could break. Revving it on muffs isn't bad because of water flow it's because the motor runs lean with no exhaust back pressure on it. Bad spark can be caused by a coil,spark plugs,spark plug wires,CDI Box or timer base or stator. You will need to do some investigating.

Yeah maybe on the first point, not so much with ya on the second.
 

CMG1039

Cadet
Joined
Apr 21, 2017
Messages
8
​Hi Guys,

So I am back with an update...sorry for the delay. Between bad weather and other plans, I haven't been able to work much on the boat and try out your theories.

First things first, I did another compression test. This was the first I have tested it since replacing a head gasket almost two years ago. Have used it only a couple of times since then so I was relatively confident this would not be an issue. All compression came back fine in the 145 range per cylinder. There was nearly no variance between cylinders.

Next, I tested the spark. Cylinder #1 failed the spark test, Cylinders #2 and #3 were fine. I swapped the spark plug wire from the failed cylinder #1, with that on on the working Cylinder #2. The wire from Failed Cylinder #1, worked on cylinder #2, so I know it was not the spark plug wire. Next I swapped the coil pack from Failed Cylinder #1 with that from the working cylinder #2. Coil Pack from Failed Cylinder #1 worked on Cylinder # 2, so I know it is not the coil pack.

I then pulled what i believe to be a ground wire (excuse my novice abilities and knowledge, see linked YouTube video below of me pointing to it) from Cylinder one coil pack. The wire ran from the Power pack to the coil pack. The connector looked to have some corrosion which I brushed up with a wire brush. I reconnected and tested spark again on Failed Cylinder #1. I got spark and Cylinder #1 now passed the test. Much like Watermann suggested, it was probably operating on 2 out of 3 cylinders. I grew optimistic. I now needed to put the boat in the water and test her out.

So I went to a local lake and put the boat in. Started right up, idled fine, engaged into gear fine, motor sounded smooth and like I know it to be when operational. So I pull away from the launch slowly and the boat is moving as it should. I get it throttle to about the half point and all is well. I decide to push it beyond the halfway throttle mark and get to about 2/3 throttle and beyond where it limits out. I am experiencing the same issue still. The boat will typically go about 25 mph when running right and full throttle, and I am going about 7.3 mph according to my Lowrance. See linked YouTube video below. About 5 seconds into the video when I try to give it full throttle, you will undoubtedly hear the motor limit out.

So what is the issue now? What should I test? A couple of thoughts in my head.... carburetor jet is clogged and not giving fuel? Could my fuel line be having issues supplying fuel to the motor? My latest thought is, could the motor be thinking it is overheating and running itself in a S.L.O.W. mode to prevent it from overheating further? Any thoughts would be greatly appreciated! This is certainly aggravating as is the life of owning a boat!

https://www.youtube.com/watch?v=XrUpt--07E8 <----Me, showing corroded wire I brushed up which ultimately gave Cylinder #1 spark. Is this a ground?

https://www.youtube.com/watch?v=Ub8wU8LYbbo&feature=youtu.be <----Motor in the water when I try to give it full throttle.
 

flyingscott

Fleet Admiral
Joined
Apr 8, 2014
Messages
7,985
That is the rpm where S.L.O.W mode will limit RPMs because it thinks something is wrong with the motor, such as overheating, low oil, no oil. It will cause the motor to misfire like yours is and not allow it to rev up.
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
36,033
Was the corroded wire " orange / blue stripe " on # 1 cylinder ?---Run with a timing light and see how spark behaves on all 3 leads.---What are the actual compression numbers ?---When was water pump service done ?
 

CMG1039

Cadet
Joined
Apr 21, 2017
Messages
8
That is the rpm where S.L.O.W mode will limit RPMs because it thinks something is wrong with the motor, such as overheating, low oil, no oil. It will cause the motor to misfire like yours is and not allow it to rev up.


Flyingscott, that's where I thought you were going with that one. I will have to take it to the water again and take a look...more and more that is what I feel like is going on. I have plenty of oil and I also know it is not overheating. I am constantly checking by hand the water discharge from the motor and it is always as cool as the water going in. If I know it is not overheating and oil is fine, what should I be checking to see that it is giving the false alarm?
 

CMG1039

Cadet
Joined
Apr 21, 2017
Messages
8
Was the corroded wire " orange / blue stripe " on # 1 cylinder ?---Run with a timing light and see how spark behaves on all 3 leads.---What are the actual compression numbers ?---When was water pump service done ?


Hi Racerone,

The corroded wire (from a still image i am looking at) looks to be orange beneath the black insulator. I do not see a blue stripe. I will have to test with a timing light. The compression numbers were consistently across all 3 cylinders in the 145-150 psi range. I haven't done the water pump in 3-5 years, but I seem to have good water pressure exiting the motor and the temperature of the water is as cool as the water body before entering the motor. I check it regularly by hand so not to rely on an alarm.
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
36,033
I have a 1995 model 70 hp block apart right now.-----Bottom cylinder sleeve has rotated and is blocking the proper air flow through the ports.
 
Top