1978 Johnson 70hp being a bi**h

68glasspar7870 · May 6, 2021

I purchased a 68 glasspar for $200 and a case of beer. The boat came with a 68 evenrude 75hp that has something living it it. I scrapped the motor and bought a 78 Johnson 70hp for $700. It runs great out of water, but does not have much power in the water. I now have the carbs apart and have been cleaning them. All the jets seemed clean upon first inspection. I have used compressed carb cleaner and a air compressor with a high output air nozzle to blow the jets out. I have ordered a carb repair kit from inlays.com. I have replaced the spark plugs. Is there anything I should check specifically before reassembling and installing g the carbs? I am also getting around 110-115psi from each cylinder. I know that’s not great, but it’s still running. I have pictures and videos I will try to post.
The motor is a 70EL78C
The carbs are 322239

DaleH · May 6, 2021

Random thoughts ... where compression looks fine to me.

Power - Not much power ... as in how?
...
Plugs - Gap looks huge, set to 0.030" regardless of what a book says and use the correct plug (check)!
...
Carbs - Comp air into carb can be the worst; one ALWAYS cleans a carb from tiniest orifice and out to the next larger and so on to the largest ...
...
Carb Cleaning - If were mine, rebuild kit or not, I'd reassembly, start IN WATER and would run through pre-mix gas mix, < 1-gallon fuel in tank, with a can of Seafoam added. Run for 10-15 minutes and shut off for at least 15-minutes. Repeat, repeat, repeat ... so bring a book or a few magazines, or have projects to do, as it WILL take a while!
...
Carb Cleaning & Decarb - Read here, last post, PLUS the one linked: https://forum.tinboats.net/viewtopic.php?f=4&t=45477&p=456535&hilit=dunk+decarb#p456535
...
Butterfly Plates - Ensure fully closed @ lowest speed, open fully @ WOT
...
Other - Sounds like an OEM Factory Service Manual would help you out ... see the link to Service Manuals in the Motors section, do not rely on a Clymer or Seloc manual for anything less than spare toilet paper ...
...
Runs - Never rely on muff testing for anything much beside 'she'll run', as without adequate backpressure, the rest of any diagnosis is limited

68glasspar7870 · May 6, 2021

New spark plugs were verified and gap is correct. Those old plugs are long gone. It doesn’t have any power as in it does not like to idle when put into gear, and falls on its face. WOT feels like I strapped a 5hp motor to the boat. Basically it sounded like a four stroke, or an extremely unhappy two stroke with fouled out plugs. It doesn’t even drop the back of the boat into the water, let alone go fast enough to plane out. I have a very short video of it running in the water at WOT and it’s not good.

MrGiggles · May 6, 2021

68glasspar7870 said:
New spark plugs were verified and gap is correct. Those old plugs are long gone. It doesn’t have any power as in it does not like to idle when put into gear, and falls on its face. WOT feels like I strapped a 5hp motor to the boat. Basically it sounded like a four stroke, or an extremely unhappy two stroke with fouled out plugs. It doesn’t even drop the back of the boat into the water, let alone go fast enough to plane out. I have a very short video of it running in the water at WOT and it’s not good.

Sounds like it is down a cylinder.

While it's running, pull a plug wire one at a time with insulated pliers, see which one is not firing. Then you know where to look.

old_fart · May 7, 2021

MrGiggles said:
Sounds like it is down a cylinder.

While it's running, pull a plug wire one at a time with insulated pliers, see which one is not firing. Then you know where to look.

And then buy 3 new coils?

Disconnecting the secondary (i.e. plug wire) while running stresses the insulation on the secondary (inside the coil), really stresses it...
Those motors use high energy ignition and can develop much higher voltage than a Kettering ignition (i.e. points), the spark
plug is needed to limit the voltage. The plug will usually arc over (i.e. spark) at a (relatively) low voltage. If it's
badly fouled the carbon will bleed off energy and prevent the secondary voltage from rising too far.
An open plug wire allows the secondary voltage to "skyrocket" which is not at all good for the insulation in the coil.
Once the insulation breaks down, the spark is quite happy to jump inside the coil (which sucks if it starts to occur
on a Sunday afternoon

.

Maybe find yourself a 3 or 4 position spark tester and set it to 1/4" or so and simply crank while looking for spark,
then you're not so mean to the poor coils. Back in the stone age (when they built those motors), you could get a
slick neon spark tester. Hold one end on the outside of the plug wire and it would blink when the plug fired (I've
got no idea why you didn't get "nailed" when that little bulb blinked, but it worked very well).

-W

RaisedByWolves · May 7, 2021

old_fart said:
MrGiggles said:

Sounds like it is down a cylinder.

While it's running, pull a plug wire one at a time with insulated pliers, see which one is not firing. Then you know where to look.

Click to expand...

And then buy 3 new coils?

Disconnecting the secondary (i.e. plug wire) while running stresses the insulation on the secondary (inside the coil), really stresses it...
Those motors use high energy ignition and can develop much higher voltage than a Kettering ignition (i.e. points), the spark
plug is needed to limit the voltage. The plug will usually arc over (i.e. spark) at a (relatively) low voltage. If it's
badly fouled the carbon will bleed off energy and prevent the secondary voltage from rising too far.
An open plug wire allows the secondary voltage to "skyrocket" which is not at all good for the insulation in the coil.
Once the insulation breaks down, the spark is quite happy to jump inside the coil (which sucks if it starts to occur
on a Sunday afternoon .

Maybe find yourself a 3 or 4 position spark tester and set it to 1/4" or so and simply crank while looking for spark,
then you're not so mean to the poor coils. Back in the stone age (when they built those motors), you could get a
slick neon spark tester. Hold one end on the outside of the plug wire and it would blink when the plug fired (I've
got no idea why you didn't get "nailed" when that little bulb blinked, but it worked very well).

-W

I doubt that pulling a wire for a short 3-4 second check would do any harm, but alternately you could always ground one wire at a time to do this check.

Any neon lamp will give a sympathetic flash when held to a spark plug.

MrGiggles · May 7, 2021

old_fart said:
MrGiggles said:

Sounds like it is down a cylinder.

While it's running, pull a plug wire one at a time with insulated pliers, see which one is not firing. Then you know where to look.

Click to expand...

And then buy 3 new coils?

Disconnecting the secondary (i.e. plug wire) while running stresses the insulation on the secondary (inside the coil), really stresses it...
Those motors use high energy ignition and can develop much higher voltage than a Kettering ignition (i.e. points), the spark
plug is needed to limit the voltage. The plug will usually arc over (i.e. spark) at a (relatively) low voltage. If it's
badly fouled the carbon will bleed off energy and prevent the secondary voltage from rising too far.
An open plug wire allows the secondary voltage to "skyrocket" which is not at all good for the insulation in the coil.
Once the insulation breaks down, the spark is quite happy to jump inside the coil (which sucks if it starts to occur
on a Sunday afternoon .

Maybe find yourself a 3 or 4 position spark tester and set it to 1/4" or so and simply crank while looking for spark,
then you're not so mean to the poor coils. Back in the stone age (when they built those motors), you could get a
slick neon spark tester. Hold one end on the outside of the plug wire and it would blink when the plug fired (I've
got no idea why you didn't get "nailed" when that little bulb blinked, but it worked very well).

-W

You are right, but a few snaps isn't going to hurt it. Obviously you shouldn't just let them hang and arc internally while you work on the engine. Just pull them off very quickly and then snap them back on, listening for a change in engine speed during the process.

There are better ways for checking spark, but this test isn't only for that, it's checking for cylinder contribution, of which there is no other easy way on a carbureted outboard.

Pappy · May 7, 2021

Okay lets start at the beginning......again.
The folks are on the right track with this but lets be a bit more specific.
NO POWER - Describe exactly what you are talking about. Does it stall if you advance the throttle to plane the boat?
Does it just kind of "go to sleep" and die at idle in gear? Meaning does it slow down steadily until it stalls? In the water I am talking about. Keep track of this comment by the way.
What propeller do you have. This is a basic question that has not been asked.
YES - you can pull the plug wires off the plugs one at a time for long enough to check the cylinders however the 49Cu In 3-cylinder will usually fool you on the center cylinder at idle in gear. Note....this should be done in the water tied to a dock unless you can hear a cylinder not firing on the hose.
You mentioned a carb kit but not what kind of kit. OEM? Hope so because that is the only complete kit available. Did you pull the welch plugs on the tops of the carbs to verify the idle pick up tubes are clean? Did not see this in the photos and you cannot verify with air or pressurized fluid. They have to be drilled and popped out. Be very careful while drilling not to bottom out and damage a calibrated idle orifice at the bottoms of the pockets.
Give us an update so we can go from here.

68glasspar7870 · May 18, 2021

Update. The new OEM carb rebuild kit came in and was mostly installed. There were caps in there that I was not going to attempt to drill out. I installed everything and now it does mot like to start and when it does the idle skyrockets. I am throwing in the towel and bringing it to a mechanic. I was not born in the carburetor era and I cannot work on them to save my life. Any time I touch a carb, the **** thing never runs again. If the mechanic tells me what I did wrong, I will keep everyone update. However, I need a part that doesn’t seem to exist on diagrams. Pics below. A part number would be appreciated. The catch is that the part is not in the picture. It is a plastic grommet that fell apart. It holds the rod in the picture.

Pappy · May 18, 2021

Go to Marine engine.
Find the 1978 70hp catalog
Go to Cylinder and crankcase
Part #44 and part #45 are what you are looking forr.

68glasspar7870 · May 20, 2021

Thanks, pappy. The price was a little ridiculous, bust out another thousand, huh? Thanks for the help!

68glasspar7870 · Aug 23, 2021

Alright. It’s been a long time since I have posted.
I personally hate it when a forum doesn’t specify what the problem was, and no one hears from the publisher again.

I decided to drop it off to a local mechanic that said he could get to it in a couple days, but it sat untouched for two months until I lost my patience and picked it up. That is why is has been so long since I have had any updates.

I dropped it off to another guy, and he fixed it in an hour. I rebuilt the carbs, and when I did that, he said I had really thrown all the carburetors out of sync. He said he did all he could do and sent me on my way. I took it to the lake and it started right up, but when I put it in gear it kept stalling. The idle was to low, and the johnson hates to run when it’s cold. I mean it stalls when it is put in gear until it warms up. So when I did let it warm up and start to move, it wouldn’t move very fast, it was hardly faster than a 7.5hp johnson on an aluminum flat bottom. So I started looking at the carbs and then I decided to back the governor screw out 3 full turns. When I did that, it made a tremendous difference. It actually throws a small rooster tail now. It could still use a little tuning to work out the cold start issue. I believe it’s getting to much fuel still and it’s flooding when it’s trying to start.

I believe if I put new carbs on the engine, it would run significantly better.

The pictures are of the Glasspar sitting after 2 months, pictures of the access fuel in the carbs, how the engine was running when I first put it in the water vs how it ran after backing out the governor screw.

MrGiggles · Aug 23, 2021

68glasspar7870 said:
Alright. It’s been a long time since I have posted.
I personally hate it when a forum doesn’t specify what the problem was, and no one hears from the publisher again.

I decided to drop it off to a local mechanic that said he could get to it in a couple days, but it sat untouched for two months until I lost my patience and picked it up. That is why is has been so long since I have had any updates.

I dropped it off to another guy, and he fixed it in an hour. I rebuilt the carbs, and when I did that, he said I had really thrown all the carburetors out of sync. He said he did all he could do and sent me on my way. I took it to the lake and it started right up, but when I put it in gear it kept stalling. The idle was to low, and the johnson hates to run when it’s cold. I mean it stalls when it is put in gear until it warms up. So when I did let it warm up and start to move, it wouldn’t move very fast, it was hardly faster than a 7.5hp johnson on an aluminum flat bottom. So I started looking at the carbs and then I decided to back the governor screw out 3 full turns. When I did that, it made a tremendous difference. It actually throws a small rooster tail now. It could still use a little tuning to work out the cold start issue. I believe it’s getting to much fuel still and it’s flooding when it’s trying to start.

I believe if I put new carbs on the engine, it would run significantly better.

The pictures are of the Glasspar sitting after 2 months, pictures of the access fuel in the carbs, how the engine was running when I first put it in the water vs how it ran after backing out the governor screw.

There is no governor on these motors. Do you mean the stops for the ignition timing? Those need to be set properly with a timing light, doing it by ear or by feel will result in a newly ventilated piston.

Pappy · Aug 23, 2021

How large is the boat and what prop are you running?
What is your average load onboard?

68glasspar7870 · Aug 24, 2021

Mr.giggles, I would definitely call it a governing screw. You have the throttle/timing arms, and there are two set screws that control how far those arms can move exactly. The bottom screw controls low end idle speed, and the top one controls how far you can push the throttle.

Pappy, the boat is approximately 16’ with 350lbs on board tops.

68glasspar7870 · Aug 24, 2021

I am not sure which prop is on it.

Pappy · Aug 24, 2021

Well.....that is a great place to start.
All too often in these forums folks will guide you down this path or the other with very little reason to back it up.
That particular engine is only 49ci. As such it has to be run at or slightly above 6000 to get the performance you want out of it.
It is and always has been a very weak performer on the bottom end. Put it on a flat bottom boat and it would be fine, A V bottom....different story, Bass boat? Even worse.
So.....always good to start at the basics instead of looking at the engine all the time.
Find out what you have for a prop.

68glasspar7870 · Aug 25, 2021

That numbers on the prop read “13 3/4 x 15” and the number, which I assume is a part number, looks to be 391198. The prop has seen better days. Pictures below.

Side note, does 24 knots sound about right for this motor? Obviously the motor does not come with a tachometer, but by the sounds of it, i am hitting high RPM’s with good top end power. Honestly I thought it was going to be faster on my tiny boat. I was expecting it to be even a little dangerous. Don’t get me wrong, it’s my first boat, and it’s a good boat to start on. I just thought it was going faster than 28MPH.

I guess I can’t complain for having just over $1100 into the whole project so far.

Pappy · Aug 25, 2021

You can have a great performing engine that, when coupled to a junk propeller, will give you poor performance.
I would start there, get a tachometer even if it is just a "tinytach" and get some baseline numbers you will need. Trim angle is important and usually the best trim angle will make the hole shot suffer some. If you have trim and tilt that is a non issue.

68glasspar7870 · Aug 26, 2021

I do not have any electronic adjustments such as tilt or trim.

Pics of the prop are attached below.

1978 Johnson 70hp being a bi**h

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