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1980 Johnson 70hp dies under load

L

Luvzlivin

New member
This motor is driving me crazy. It runs excellent with the muffs on but when I put it in the lake it just dies when I put it in gear. It seems like a fuel problem but I have thoroughly cleaned the carbs and, like I say, it runs like a top with the muffs on. Any help is appreciated. I have about 130 psi compression on all cylinders. Spark is good. Timing hasn’t changed. Fuel pump is pumping. I am truly stumped.
 
This is going to sound nuts but it is a similar problem I had with a 90 hp 80’s model. Compression was good and sounded fine until it was in the water and then wouldn’t go under a load. The brand new plugs I had put in all four cylinders I decided to pull at look at. Two of those had never fired. Ever. After a dozen times in the tank and muffs. Never could tell. Until I pulled the plugs. Mine was a four cylinder so I moved the sparking coils to the non sparking side and made no difference. As it turns out the stator beneath the flywheel had cracks in it not putting out enough power with all the leaks. Replaced the stator and now all 4 cylinders have good spark. Now you stated you have good spark so I’m assuming that means each plug. If you didn’t check them all you might have my issue.
 
Sfox said:
This is going to sound nuts but it is a similar problem I had with a 90 hp 80’s model. Compression was good and sounded fine until it was in the water and then wouldn’t go under a load. The brand new plugs I had put in all four cylinders I decided to pull at look at. Two of those had never fired. Ever. After a dozen times in the tank and muffs. Never could tell. Until I pulled the plugs. Mine was a four cylinder so I moved the sparking coils to the non sparking side and made no difference. As it turns out the stator beneath the flywheel had cracks in it not putting out enough power with all the leaks. Replaced the stator and now all 4 cylinders have good spark. Now you stated you have good spark so I’m assuming that means each plug. If you didn’t check them all you might have my issue.
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Pulled the plugs with the muffs on and they are all firing. Not sure if it’s changing in the water or not… the stator DOES have a couple of cracks in it. COULD be it maybe. Although I am not understanding what that would actually do to cause an issue?
 
Luvzlivin said:
Pulled the plugs with the muffs on and they are all firing. Not sure if it’s changing in the water or not… the stator DOES have a couple of cracks in it. COULD be it maybe. Although I am not understanding what that would actually do to cause an issue?
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What I was told by my mechanic is if they are cracked they leak power and often around a crack you will find black ooze or a goo. I’m told that is the insulation breaking down.
 
How did it run for you last season?-----Does spark jump a gap of 3/8" on a test device?------High speed jet ( orifice plug ) in the very bottom of float bowl clean ?----Fuel pump diaphragm checked?
 
Having somewhat the same issue with a 1979 70hp. Runs great with muffs. Does not want to idle under load, idle forward or reverse dies every time. But get it going it runs like a top at 3/4 throttle. This motor was sitting for a long time before i got it so i am starting with carb rebuilds. Did check TDC looks good and plugs are good, so i will see
 
racerone said:
How did it run for you last season?-----Does spark jump a gap of 3/8" on a test device?------High speed jet ( orifice plug ) in the very bottom of float bowl clean ?----Fuel pump diaphragm checked?
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It did not run for for or five years. Cleaned the stator up and it has excellent spark now. I can actually keep it running in the lake now but still runs like ****. I need to play with the choke to keep it going which still seems like a plugged jet problem yet I KNOW they aren’t plugged. Probably gonna check them AGAIN I guess… it sure is acting like carbs but yet I think they are clean
 
RGC-----First thing is to post compression , actual values.----They can all run great on muffs on 2 of 3 cylinders.----Does spark jump a gap of 3/8" or more on a test device?----Motor has a history of water leaks from exhaust manifold gaskets.-------And if motor sat for a long time the high speed jet ( orifice plug ) may need to be cleaned.-----You must make sure that carburetors are clean as carburetors are also the " oil pump " on this motor.-----If a high speed jet is plugged you risk major damage to a cylinder.
 
RGC said:
Having somewhat the same issue with a 1979 70hp. Runs great with muffs. Does not want to idle under load, idle forward or reverse dies every time. But get it going it runs like a top at 3/4 throttle. This motor was sitting for a long time before i got it so i am starting with carb rebuilds. Did check TDC looks good and plugs are good, so i will see
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For me I don’t see how the timing could have changed on this motor although it could be a potential part of the problem for me here too I suppose. Not easy to check timing for me without a tach though
 
It think the spark tester is 7/16 but after cleaning the stator it worked like a damn on all three cylinders. All orifices are clean as are the screens in the fuel pump. I am gonna recheck the mains again today as I did find a blockage in the main tube between the high speed and idle orifices on the top carb last night but the other two were blowing through okay although I will check them again as it’s still acting like it’s a fuel starvation problem. Good fuel pressure on all three cylinders (checked by popping a hose off the carb).
 
I can not see , hear or touch your motor.----If you answer questions posted you will get results.-------For me the trouble shooting on these simple motors was learned 50 years ago.
 
Ok. So I found one reed that I could see daylight through. I got it to seat. I put the carbs in an ultrasonic for a bit in case there was anything I missed cleaning. I can get it to run and stay running under load now but it runs terribly. Seems to go back and forth from running on one or two cylinders to running on all three) I noticed quite a bit of fuel coming out of that hose on the bottom of the motor. (I think it’s supposed to attach somewhere to recycle the excess fuel but I cannot see where it goes…).
 
racerone said:
I can not see , hear or touch your motor.----If you answer questions posted you will get results.-------For me the trouble shooting on these simple motors was learned 50 years ago.
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Sorry if I didn’t answer. I don’t know about diaphragms in fuel pump. I did check the screen and it was clear. I disconnected each hose off the carbs while running and it is pumping lots of fuel to them
 
racerone said:
RGC-----First thing is to post compression , actual values.----They can all run great on muffs on 2 of 3 cylinders.----Does spark jump a gap of 3/8" or more on a test device?----Motor has a history of water leaks from exhaust manifold gaskets.-------And if motor sat for a long time the high speed jet ( orifice plug ) may need to be cleaned.-----You must make sure that carburetors are clean as carburetors are also the " oil pump " on this motor.-----If a high speed jet is plugged you risk major damage to a cylinder.
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I think I answered all but the compression question here which is all 3 cylinders are just over 130 psi - 132 ish
 
I am also thinking of opening exhaust manifold up to see if anything is plugged there and stopping it from breathing properly as it seems that everything on the intake side is in order. Except this possible over fueling issue
 
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