15 hp Johnson no power

[Johnson209]

Im new here and I heard this place is good site if I needed some help. I hope you guys can help me out all imputs appreciated.I have 1975 15 hp Johnson. My sparks jumps at 1/4 both plugs and are bright blue. Compression tested at 25 to 35 on each cylinder. The test wasn't accurate because the tester I had was to long and wasn't plug in all the way due to piston hitting it. okay so here's were I'm at. The motor starts and idles great with 2 to three pulls. Does not die or putter. I can troll the whole day without any problems but at wide open throttle im only getting up to 9 to 10 mph. I am running at 2 cylnders I think ,because when I run the motor and unplug each plugs at a time the motor does dies out and doesnt stay rumning. The prop isnt bent nor does it slipp. It does plane out and runs great. But the power isn't there. I check the plugs and it seems to have water on the bottom cylinder, the plugs are wet .
I'm just a novice and know little Bout outboard motor but willing to take on a challenge if it isn't too hard. So what am I looking at. Do I have a bad head gasket if so how do I change it? Or is there other things that I have to look at. Any ideas are welcome.

Thanks for looking and I
Hope you guys can help out.

 

[nwcove]

Re: 15 hp Johnson no power

the first thing you need to do is a proper compression test. and post back with numbers.

you also say that if you pull a plug wire the engine wont stay running? does this happen with both plugs, or just one?

 

[Johnson209]

Re: 15 hp Johnson no power

the first thing you need to do is a proper compression test. and post back with numbers.

you also say that if you pull a plug wire the engine wont stay running? does this happen with both plugs, or just one?

I did it with both plugs. I Pull the top plugs while running the engines and it dies. Replug the top plug and started the engine and did it to the bottom plugs, it also kill the engine.

I will post compression number ASAP when I get a chance to buy a different tester.

 

[nwcove]

Re: 15 hp Johnson no power


you sure you dont just have the wrong adapter on the tester? normally you just use the tester, without any adapter . have a look at it, might just be a matter of removing the extension and yer good to go for the test.

 

[Johnson209]

Re: 15 hp Johnson no power

you sure you dont just have the wrong adapter on the tester? normally you just use the tester, without any adapter . have a look at it, might just be a matter of removing the extension and yer good to go for the test.[/


Thks for the pics, I never even thought of that. I let you know how it goes if my tester can do that, if not I'm off to a auto parts store.

 

[Johnson209]

Re: 15 hp Johnson no power

you sure you dont just have the wrong adapter on the tester? normally you just use the tester, without any adapter . have a look at it, might just be a matter of removing the extension and yer good to go for the test.[/


Here my numbers #
90 on top cylinders and 95 on the bottom, is that normal or too low ?

Thks

 

[OptsyEagle]

Re: 15 hp Johnson no power

The compression is fine.

Does the carbs cam follower (the little roller that controls the carbs throttle) touch the throttle cam (the metal piece that pushes on that roller when you turn the throttle grip) at exactly on the arrow that is indented in the throttle cam? This is to sinc up your timing advance when you are running at higher RPMs.

 

[Johnson209]

Re: 15 hp Johnson no power

The compression is fine.

Does the carbs cam follower (the little roller that controls the carbs throttle) touch the throttle cam (the metal piece that pushes on that roller when you turn the throttle grip) at exactly on the arrow that is indented in the throttle cam? This is to sinc up your timing advance when you are running at higher RPMs.

Thanks for the imput optsy, I check the motor and the carb cam follower does touch and match up with the arrow on the throttle cam when it's in the shift position if that's what you mean ?

 

[OptsyEagle]

Re: 15 hp Johnson no power

Hmmm. So lets see. You have good spark on both cylinders and acceptable compression, but the motor cannot run on either cylinder alone and you get no top end. Obviously you have weak cylinders as opposed to dead ones. You said that you have noticed water in the bottom cylinder. That water, if it is present, would most likely be coming through the head gasket so I would probably take the next step and pull the head for a look. I am surprised that the compression would be there when you have a gasket leak, but it is possible.

Moving away from the water issue, it is also possible that your carburetor's air vent is clogged up and doesn't allow enough venting to pull the maximum fuel up the high speed jet, that is required for top end performance. I believe the air vent in your carb is that open channel in the upper left side of the carb. (maybe others may correct me on this if I am wrong). You could take a look to see if there is any obstruction and even think about a carb. cleaning to be sure. It may also be a clogged high speed jet in the carb., but that would not explain why it will not run on either cylinder, at idle, which it should.

My next thought would be the upper and lower crankcase seals but it would be quite the coincidence that both would go at the same time. However, what might be the case is that the upper crankcase seal was degraded, but was unnoticeable until the lower cylinder started failing due to water entry.

The other thing that can make for a weak cylinder is the points gap. How long has it been since you have re-set those points. Since the rub bars do wear down, if the upper cylinders gap was reduced enough, the cylinder would run but may not run well enough to keep the motor running on its own. The point gap determines the timing of the spark and a reduced gap will see the cylinder firing past top dead center and hence not provide the umpff, it should. If we ignored the water observation, if both point gaps were very low (should be 0.020") you may find that it will start and idle all day but suffer at the top end.

Anyway, those are my thoughts.

 

[2manband]

Re: 15 hp Johnson no power

When you say that one of the plugs is wet - are you sure that it's water and not gas?

Usually water in the cylinder will create a milky residue when it mixes with the gas/oil. It doesn't come out looking clear like drinking water.

I agree that it would be strange to have compression numbers that good while leaking water into the cylinder. Not impossible, I suppose, but pretty unusual.

If your plugs are wet with fuel, then there's a good chance that you're not getting spark.

 

[kbait]

Re: 15 hp Johnson no power

Check for lateral play in the armature plate. The amount of slop will directly affect point gap, and timing. If there's much slop at all, it'll never run correctly.. but it can be stabilized.. Post back if this is an issue.

Also, in my experience, those '74-'76 9.9/15hp motors like NGK plugs better than the recommended Champions.. NGK B7HS gapped @ .030".

 

[Rick.]

Re: 15 hp Johnson no power

You're getting lots of excellent advice above. All things well worth follow up. I would add the water might be getting into the lower thru the exhaust plate gasket. A lack of carb. suction could also be bad carb to manifold gasket and/or a bad intake manifold gasket. Best of luck. You will find your problem but some times it isn't just one thing. Rick.

 

[Johnson209]

Re: 15 hp Johnson no power

Hmmm. So lets see. You have good spark on both cylinders and acceptable compression, but the motor cannot run on either cylinder alone and you get no top end. Obviously you have weak cylinders as opposed to dead ones. You said that you have noticed water in the bottom cylinder. That water, if it is present, would most likely be coming through the head gasket so I would probably take the next step and pull the head for a look. I am surprised that the compression would be there when you have a gasket leak, but it is possible.

Moving away from the water issue, it is also possible that your carburetor's air vent is clogged up and doesn't allow enough venting to pull the maximum fuel up the high speed jet, that is required for top end performance. I believe the air vent in your carb is that open channel in the upper left side of the carb. (maybe others may correct me on this if I am wrong). You could take a look to see if there is any obstruction and even think about a carb. cleaning to be sure. It may also be a clogged high speed jet in the carb., but that would not explain why it will not run on either cylinder, at idle, which it should.

My next thought would be the upper and lower crankcase seals but it would be quite the coincidence that both would go at the same time. However, what might be the case is that the upper crankcase seal was degraded, but was unnoticeable until the lower cylinder started failing due to water entry.

The other thing that can make for a weak cylinder is the points gap. How long has it been since you have re-set those points. Since the rub bars do wear down, if the upper cylinders gap was reduced enough, the cylinder would run but may not run well enough to keep the motor running on its own. The point gap determines the timing of the spark and a reduced gap will see the cylinder firing past top dead center and hence not provide the umpff, it should. If we ignored the water observation, if both point gaps were very low (should be 0.020") you may find that it will start and idle all day but suffer at the top end.

Anyway, those are my thoughts.

A lot of info... I appreciated Thks a ton.
I was thinking the point gap also. I bought this motor last year and never Check on it before because it starts and runs fine. But before I start tearing the motor up and replacing gasket Ill start with the easy project by cleaning the carb, replacing sparks plugs, decarbonizing and replacing points and gaps since Its only a couple bucks. How do I set points gaps on this motor? I had a 1956 Johnson and set gap on that motor before but forgotten its been over tens years now. Any direction will help Thks again.

 

[Johnson209]

Re: 15 hp Johnson no power

Well it's Not A milky residue,it looks more like tiny oil spots on water and it's clear. Ill try replacing my old gas with new and see if I can stil see water on sparks.

Keep it comming guys ... All info are really helpful
Thks a ton

 

[Johnson209]

Re: 15 hp Johnson no power

Check for lateral play in the armature plate. The amount of slop will directly affect point gap, and timing. If there's much slop at all, it'll never run correctly.. but it can be stabilized.. Post back if this is an issue.

Also, in my experience, those '74-'76 9.9/15hp motors like NGK plugs better than the recommended Champions.. NGK B7HS gapped @ .030".

Ok... I'll save my champ plugs for back ups and buy some ngk plugs.. How much slop am I looking for? How do I check for play in the armature plate? Is that the throttle cam were it touches the roller cam. It seems to push the roller all the way down when I have it on wot.

 

[Johnson209]

Re: 15 hp Johnson no power

Update, I change my plugs to ngk and set to .30. Also Clean the carb and reuse old gasket. It takes more then 3 to 4 pulls to get started now. Worst then before. I check plugs for water residue and there was none. Maybe I just had water in my old tank. I will be testing the motor tommorow on the river to see how it really runs.
Thks for all help

I will post feedback ASAP

 

[OptsyEagle]

Re: 15 hp Johnson no power

How do I set points gaps on this motor? I had a 1956 Johnson and set gap on that motor before but forgotten its been over tens years now. Any direction will help Thks again.

You will first need to pull the flywheel off. This is done by loosening the center bolt, but not removing it. The flywheel then is removed using a 3 prong puller. The center bolt is left on because when the flywheel pops off, it pops and you do not want it to fly off onto the floor, or worse your toe.

Now put it in gear and using the propeller, turn the cam until the point's rub bar is on the "set" mark of the cam (when turning the propeller always turn it so the cam turns clockwise when looking down at it. never turn it the other way, if you can avoid it). With a feeler guage, check what gap is currently there. Do this with both points. Now you simply unscrew the slotted screw that is on the point. Near the outer edge of the point there is a groove. Use another screw driver and push on this to widen the gap. Tighten the slotted screw snuggly and re-check the point gap. It should allow a 0.020" feeler guage to pass through it and not allow a 0.022" feeler to go through. Do this for both points. I usually turn the propeller for a few revolutions and then check it again to ensure they stay at 0.020". Then clean them by pulling a clean business card, dipped in laquer thinner, through the points and blow with compressed air. You are pretty much done here. If the points are all pitted, then they should be replaced. There is also a wick that is pushed up against the cam. You should add about two drops of motor oil to this wick. Not too much because you don't want oil flying around in there, dirtying up your clean points, but it will lubricate the cam and reduce wear and reduced wear allows your points to maintain their gaps, longer.

Now ensure the flywheel key is in place and put the flywheel back on. Snugg up the center bolt. Now with a torque wrench torque that down to 47.5 ft/lbs and you are now back in business.

You will also need a strap wrench of some sort to ensure the flywheel doesn't turn when you are loosening the center bolt and torquing it back on. In lieu of a strap wrench, I have used a piece of electrical cord, wrapped around the flywheel with both ends secured to a piece of very strong wood (anything less then 1" thick will most likely break from the torque you will be using).

 

[Johnson209]

Re: 15 hp Johnson no power

You will first need to pull the flywheel off. This is done by loosening the center bolt, but not removing it. The flywheel then is removed using a 3 prong puller. The center bolt is left on because when the flywheel pops off, it pops and you do not want it to fly off onto the floor, or worse your toe.

Now put it in gear and using the propeller, turn the cam until the point's rub bar is on the "set" mark of the cam (when turning the propeller always turn it so the cam turns clockwise when looking down at it. never turn it the other way, if you can avoid it). With a feeler guage, check what gap is currently there. Do this with both points. Now you simply unscrew the slotted screw that is on the point. Near the outer edge of the point there is a groove. Use another screw driver and push on this to widen the gap. Tighten the slotted screw snuggly and re-check the point gap. It should allow a 0.020" feeler guage to pass through it and not allow a 0.022" feeler to go through. Do this for both points. I usually turn the propeller for a few revolutions and then check it again to ensure they stay at 0.020". Then clean them by pulling a clean business card, dipped in laquer thinner, through the points and blow with compressed air. You are pretty much done here. If the points are all pitted, then they should be replaced. There is also a wick that is pushed up against the cam. You should add about two drops of motor oil to this wick. Not too much because you don't want oil flying around in there, dirtying up your clean points, but it will lubricate the cam and reduce wear and reduced wear allows your points to maintain their gaps, longer.

Now ensure the flywheel key is in place and put the flywheel back on. Snugg up the center bolt. Now with a torque wrench torque that down to 47.5 ft/lbs and you are now back in business.

You will also need a strap wrench of some sort to ensure the flywheel doesn't turn when you are loosening the center bolt and torquing it back on. In lieu of a strap wrench, I have used a piece of electrical cord, wrapped around the flywheel with both ends secured to a piece of very strong wood (anything less then 1" thick will most likely break from the torque you will be using).

Very helpful and drescriptive information, I thank you for your time. As I was about to take off the fly wheel i decided to check the air silencer to get a closer look at the cam throttle and it was off by a inch.
Here's a pics of the cam follower hitting the throttle cam. It is not line up with the arrow as you can see when it hits the throttle cam. Its off by half inch or so. Would that throw off the synch. I see two screw on it but how do i adjust it? Anyways I also RECHECK my coils and theres a crack on it. A very fine hair line crack. It wasnt there before I think.
Im thinking this might be the corperate what do u think?

 

[nwcove]

Re: 15 hp Johnson no power

hard to tell from the coil pic, but if it is cracked, replace it. the throttle cam has adjustment on the bottom side. i do see what looks like a coat hanger twisted around things..... if im seeing right,whats its purpose??

 

[Johnson209]

Re: 15 hp Johnson no power

hard to tell from the coil pic, but if it is cracked, replace it. the throttle cam has adjustment on the bottom side. i do see what looks like a coat hanger twisted around things..... if im seeing right,whats its purpose??

The coat hanger is used to retrieved my bolts. I lost 2 screw so far.
Well guess I'm gonna hold up on setting the points until I get a new coil.
I will see if I can adjust the cam.
Thks