'74 70hp Johnson Won't idle/rough running low speed

[sprcpr]

Ok, have had this motor for about a year. When I first bought this motor it wouldn't run hardely at all. Took it to a repair place and they cleaned up the carbs with carb cleaner, replaced the head gasket (water in bottom cylinder), decarbonized the head, checked compression that they reported to me as 130+ on all three cylinders. They couldn't make this motor idle and said it wasn't worth the trouble of figuring it out as it was an old motor.

I ran it last year (lousy year around here for the most part) and then this year I pulled it out and started running it. Replaced the plugs right off the bat with NGK B7HS this year and started running the motor. Same issue which is super annoying coming into or leaving the dock. The motor will run in the warmimg lever and I can bump it down and then I have to push the warming lever down with one hand and throw the motor into gear with the other hand. Catch the motor before it stalls and away we go. I can run at any speed above 4 miles per hour. The boat will run great at wide open.

After reading all of the posts on here I figured I had a fuel problem. I rebuilt the carbs, put in new carb kits as it seemed I might have a carb leaking (lot's of smoke when I started the motor). I then thought I might be dropping a cylinder as the motor shakes at idle and seems to be missing. Top coil had cracks in it and the other two look brand new. Replaced the top coil. Same problem. Damn thing just won't idle in gear. We had a chance to run it in a barrell and try to figure things out(barrel at my fathers house 100 miles away). I didn't have my book with me and so we were just guessing at things. Some things we noticed: 1. The boat seems to be running awfully rich. It smokes like hell and upon stalling and an imediate plug removal all of the plugs are fouled. There was a HEAVY amount of oil in the drum. Also I probably single handedly reduced the mosquito population by half (lots of smoke). I can pump the fuel bulb up hard when the engine is running and no change in sound or motor behavior (new fuel line last week). Fuel pump screen was cleaned with carb cleaner and put back in. I also replaced all of the fuel lines going from the fuel pump to the middle carb and all fuel lines between carbs. Also sprayed WD40 on all of the carb shafts and gaskets looking for an air leak. No difference in running was heard. Motor just kind of winds down like a clock. Again get the motor at 1/4 throttle and it picks right up. I picked up a new set of Champion plugs tonight to put in. I would like to run a hotter plug but my local car parts guy (who had the correct marine plugs) couldn't cross reference to a hotter plug. Is there a hotter plug? and how great are the risks with a step hotter? I also am very careful to run at 50:1 and probably err on the side of caution and am probably at 45:1 as I add probably 17oz of oil to 6 gallons of gas + an ounce of carbon guard. I've heard that I might want to reduce the mix a little. What's safe?

I also have sincronizing questions. I'm not sure how to sinc this motor. I have read the directions in the book and first my cam follower didn't even touch the throttle shaft at idle. I even tried to move the follower but it doesn't reach the cam. The idle screw doesn't touch the stop as well. I turned the white plastic peice that was on the throttle cam end of the link between the timing adjustment and the throttle three turns and adjusted the throttle so the roller is in position according to the book. I haven't checked timing yet to see what it is doing (I don't have a barrel at my house). I also have no idea what the adjuster on the throttle cable link does. I can turn the little thumb wheel down near where the throttle cable enters the motor housing and can change the tuning, but I have no idea what I'm looking for with this adjustment.

Thoughts? Thanks for any help.

 

[borz80]

Re: '74 70hp Johnson Won't idle/rough running low speed

To me it seems like your just getting too much oil. The mixture is right. Don't lower the mixture, you dont want to blow the motor. I had this problem before where I was dropping 1 cylinder that ran off of the lower carb. The problem ended up being that I had put the low speed jet for the 115 hp motor I have in the carb for the 85 hp I was running. I would pull your jets out and make sure they are the same size in each carb. Then if that isn't the problem, go buy ears from walmart , if you dont already have them. Then hook it to hose and put on motor to run it on land. Start it and rev it and see how it runs. If it runs good out of the water the reed valves may be bad. Had this same problem on my 115 hp. Try those two things and see what happens.

 

[sprcpr]

Re: '74 70hp Johnson Won't idle/rough running low speed

Really looked over all of the jets when I rebuilt the carbs. All of them are the same. Hoping that it isn't a reed problem. I can run all day long on the muffs.

 

[jtexas]

Re: '74 70hp Johnson Won't idle/rough running low speed

welcome to iboats!

1. 50:1 is perfect, no need for more oil, it just masks other symptoms.
2. "130+ on all three" is not specific enough. Test it yourself. If that motor has 130 psi, either it's been rebuilt or else it's in remarkably good condition.
3. "They ... said it wasn't worth the trouble..." ok, maybe not worth it to pay somebody else to fix it, but for sure worth the effort of fixing it yourself.
4. Champion QL77JC4 is the right plug. Fix what's wrong instead of masking the symptom with the wrong plug. NGK makes great plugs but your johnson wants the champions.
5. Go down to walmarts and get yourself a garden hose attachment ("muffs") so you can test run the motor without a barrel. Don't rev it up on the muffs, though, and you can't judge how well it will perform under load, but you will be able to fire it up and work on it.
6. I don't think WD40 works as a manifold leak tester any more -- they changed propellent from LPG to carbon dioxide a few years ago.

Your symptoms sound to me kinda like it's running rich, gradually flooding at idle. Like misadjusted float heights, maybe. I don't believe you have slow speed mixture needles. If you tilt the motor full up and squeeze the primer bulb, does fuel come out the carb throats?

See the image below (ignore the yellow arrow). notice the throttle rod measurement from throttle lever to yoke.

Make sure the carb butterflies are all closed at idle, parallel throughout their range of motion, and horizontal (not beyond) at WOT, and that the cam hits the roller right on the mark.

The thumbwheel adjustment on the throttle cable...use that to adjust the cable length to where the idle stop screw will butt up against the throttle lever. That screw shouldn't be all the way out or all the way in either -- make it close to the middle to start with so you have margin to adjust it either way. If you get the cable too loose, the idle speed will be all over the place. Too tight and the warmup lever will tend to rise on its own when you operate the control stick.

On the muffs, set the idle speed to about 1000, then fine tune it after you get it in the water. Should be about 850 in gear in the water.

p.s., you can open the spark plug gap up to .035 or even .040, if you're doing lots of idling or trolling.

 

[joey nathan]

Re: '74 70hp Johnson Won't idle/rough running low speed

SPR,
I have a '75 70 hp engine. It runs great, so I can tell you it is worth hanging in there to get it right. I found an online source to download the service manual and it has proved to be invaluable.

Spray carb cleaner would probably work better to check for vacuum leaks.
I agree, don't change 50:1 ratio, mine runs perfectly on 6 gallons to 1 pint.
I cured the excessive smoke thing by running a full can of SeaFoam mixed with 3/4 of a gallon of gas (de-carb procedure).
Ignition timing is probably pretty close if it runs well at speed, but it's fairly simple to verify timing is correct with a timing light.

You're on right track, idle is not set correctly if the idle adjust screw is not in contact with the arm. As suggested, set adjuster screw to its mid point, use thumb wheel on throttle cable to bring it into contact, then fine tune. This procedure is outlined in the service manual.
Good Luck...

 

[SwiftFootTim]

Re: '74 70hp Johnson Won't idle/rough running low speed

I have a 1982 Evinrude EL60CNM that I haven't been able to run at low speeds well this year either. Going to find myself a manual for it as well.

I have noticed that my throttle cable doesn't engage the engine when I lock into forward either, there is almost 30 degrees of play in the throttle before the cable engages the cam. Should I adjust this? It almost acts like my motor isn't getting any gas and just stalls out.

 

[jtexas]

Re: '74 70hp Johnson Won't idle/rough running low speed

It's got some wiggle room there when you first move the throttle control forward, so that it can shift and idle in forward gear before any increase in RPMs. Then the spark timing advance has to begin before the throttle valves open. If the idle stop screw is butted up against the throttle lever when the engine's in neutral, and the carb throttle valves are all closed at idle and perfectly horizontal (not beyond) at WOT, then the cable most likely does not need adjusting.

Don't jump to conclusions: do some basic troubleshooting and you will find the cause of your symptoms.

Best to start a new thread of your own, trying to help 2 motors in one thread is just too confusing.

 

[sprcpr]

Re: '74 70hp Johnson Won't idle/rough running low speed

Thought I'd post an update to what has gone on with this motor. I adjusted the linkage and had the motor running fine on the muffs. It will sit there and idle ( little high) all day long. I replaced the NGK plugs for Champions and then took the boat down to the ramp. Tried to start and it would start and kick backward violently every now and then (almost like it was WAY out of time). Funny thing is that it would run for a few seconds sometimes. I played around in the water for a few minutes but the dock was BUSY on a Sunday afternoon in 90 degree heat. I then pulled the boat out of the water very dejected (me not the boat) and went home. It wasn't until I was home that I realized that in replacing the plugs I had reversed the plug wires on the bottom two cylinders! I had "checked" them at the dock, but like I said I was in a hurry and stressed because the ramp was so busy. I had followed the wires with my finger, but I never actually looked because I couldn't see them clearly from within the boat.

Came home and it would be almost another week before I could get the boat out to play around some more. Pretty mush the same deal as always. It just won't idle. I can rev the snot out of it, and then it will run fine, but it just quits at idle. This thing runs great at high speed. It might run for 20 seconds just fine at idle, but then it's going to quit. No adjusting of the idle seems to help. I'm about to chalk it up as just an old motor when a young kid and his girlfriend put a boat in beside us with the oldest outboard I've seen in a LOOOOONG time. Black with a wide chrome ring around the entire motor. A friend of my dad had a motor just like that when I was a very little kid. I only remember it because I was terrified of it at the time. It always looked like a monster trying to get in the boat. The kid putts away from the dock and the motor runs FLAWLESSLY! So I can't just say it's age with my motor....

Ok, so off to look for a compression tester. I didn't want to bite the bullet and buy one as I have very little use for one these days other than the boat... and aw hell, I'm a cheap SOB at heart. But this damn motor is stuck in my head now. It seems like it is ignition dependent. Lean or rich doesn't seem to matter, and I can see that we aren't fuel starved, so that eliminates a bunch of stuff. I can shut the buterflies off in the carbs and it will die, same as iff they are cracked open a little. So while I'm buying the compression tester I buy a spark tester. It's an adjustable tool that allows you to adjust the spark gap and it's in a black plastic housing. $12 something at advanced auto. BTW, advanced has the same compression tester as Sears for about $10 less. Sears also has a really nice set for about $25 more. This morning I check the compression and get 135 across all three cylinders. Ok, the top one is about 132, but the bottom two are a solid 135. So It isn't a compression thing. I check the spark and there I notice a difference, a big difference. Top (new) coil will throw a nice 3/4" bright blue spark. Bottom two coils are intermittent and require a much smaller gap to throw a consistent spark. Also the top plug is clean and white after an hours running where the bottom two plugs are more brown, and the bottom plug is the brownest.

So I'm thinking that the bottom two coils that look newer just might not be performing as good as they look. I also tried to redo the plug end on the bottom coil thinking that maybe the wire is just corroded at the cap end, it didn't make a difference. I ordered two new coils and I guess we will see from there. I will post any updates.

 

[jtexas]

Re: '74 70hp Johnson Won't idle/rough running low speed

You can rule out coils by swapping the top & bottom, see if the problem follows.

 

[JBQIII]

Re: '74 70hp Johnson Won't idle/rough running low speed

Thought I'd post an update to what has gone on with this motor. I adjusted the linkage and had the motor running fine on the muffs. It will sit there and idle ( little high) all day long. I replaced the NGK plugs for Champions and then took the boat down to the ramp. Tried to start and it would start and kick backward violently every now and then (almost like it was WAY out of time). Funny thing is that it would run for a few seconds sometimes. I played around in the water for a few minutes but the dock was BUSY on a Sunday afternoon in 90 degree heat. I then pulled the boat out of the water very dejected (me not the boat) and went home. It wasn't until I was home that I realized that in replacing the plugs I had reversed the plug wires on the bottom two cylinders! I had "checked" them at the dock, but like I said I was in a hurry and stressed because the ramp was so busy. I had followed the wires with my finger, but I never actually looked because I couldn't see them clearly from within the boat.

Came home and it would be almost another week before I could get the boat out to play around some more. Pretty mush the same deal as always. It just won't idle. I can rev the snot out of it, and then it will run fine, but it just quits at idle. This thing runs great at high speed. It might run for 20 seconds just fine at idle, but then it's going to quit. No adjusting of the idle seems to help. I'm about to chalk it up as just an old motor when a young kid and his girlfriend put a boat in beside us with the oldest outboard I've seen in a LOOOOONG time. Black with a wide chrome ring around the entire motor. A friend of my dad had a motor just like that when I was a very little kid. I only remember it because I was terrified of it at the time. It always looked like a monster trying to get in the boat. The kid putts away from the dock and the motor runs FLAWLESSLY! So I can't just say it's age with my motor....

Ok, so off to look for a compression tester. I didn't want to bite the bullet and buy one as I have very little use for one these days other than the boat... and aw hell, I'm a cheap SOB at heart. But this damn motor is stuck in my head now. It seems like it is ignition dependent. Lean or rich doesn't seem to matter, and I can see that we aren't fuel starved, so that eliminates a bunch of stuff. I can shut the buterflies off in the carbs and it will die, same as iff they are cracked open a little. So while I'm buying the compression tester I buy a spark tester. It's an adjustable tool that allows you to adjust the spark gap and it's in a black plastic housing. $12 something at advanced auto. BTW, advanced has the same compression tester as Sears for about $10 less. Sears also has a really nice set for about $25 more. This morning I check the compression and get 135 across all three cylinders. Ok, the top one is about 132, but the bottom two are a solid 135. So It isn't a compression thing. I check the spark and there I notice a difference, a big difference. Top (new) coil will throw a nice 3/4" bright blue spark. Bottom two coils are intermittent and require a much smaller gap to throw a consistent spark. Also the top plug is clean and white after an hours running where the bottom two plugs are more brown, and the bottom plug is the brownest.

So I'm thinking that the bottom two coils that look newer just might not be performing as good as they look. I also tried to redo the plug end on the bottom coil thinking that maybe the wire is just corroded at the cap end, it didn't make a difference. I ordered two new coils and I guess we will see from there. I will post any updates.

Any updates?

 

[flyingscott]

Any updates?

from 11 yrs ago????

 

[JBQIII]

from 11 yrs ago????

I can dream can’t I