Logo
FULL SITE MENU

Johnson 4hp Overheated

Q

QAOKMSK - Mark

New member
I ran into an overheating issue yesterday. Have a 1978 Johnson 4hp. Went through all the vernaculars, new fuel line to fuel pump, new fuel pump, newfuel line to carb. Rebuilt the carb, 90 pounds of compression both cylinders, super white spark on the plugs. Dropped the lower end replaced the water pump, inspected the prop and gear assembly it was good, drained the old oil in the lower end after 20 years. And it was still pristine ish for 20 years, and put in new gear oil. I put the lower end back in, and it starts right up smoked alot but I was so happy, surprised, I didn't look to see if she was returning any water. Within 2 - 3 minutes she stopped, very hot. I could still mannually turn the prop after it cooled down, so I don't think it is seized. I failed to check the water pump before installing it back into the lower end.
What should my next step be?
Also how important is the o-ring below the shaft grooves/spline that fits into the powerhead? It didn't have one when I took it apart. Thanks in advance, 300 dollars in and still learning the school of hard knocks!
 
Why the new fuel pump?-----A new diaphragm is usually all that is needed.-----You are sure the water tube went into the outlet of the pump?-----The o-ring MUST be installed on the driveshaft.
 
Where can I geta diaphragm as now I have two pumps, I can rebuild that. Will make sure i get tube into the out let, and the o-ring. Fingers crossed the shaft comes out. Thank you
 
Diaphragm available on this site.-----Hint-----Pump was used from 1968 to 2005.-----Look for the part # on much newer models including 6 / 8 / 9.9 models.----Factory repair kit has complete instructions.----Buy one to get needed parts. ----Then just the diaphragms.
 
Thank you, much appreciated. I just dropped the lower end. The shaft came out with little resistance, pic.
Best practices to check the water pump?
Best practice to check the return tube?
Truly appreciate this page and the members 🙏.
 
It is not a " return tube " at all.-----Water goes up the tube to supply cooling water to the motor.----Water pumps are elegantly simple.-----In over 50 years I have never tested one by turning it with a drill.
 
10-4 on that, ok rubber o-ring on shaft, installed water tube correctly, closed up the motor ready to test. Side note, i have some grease at the power head that push out possibly during the overheat. Pic.
What do I need to look out for to make sure I still have a good seal?
 
racerone said:
It is not a " return tube " at all.-----Water goes up the tube to supply cooling water to the motor.----Water pumps are elegantly simple.-----In over 50 years I have never tested one by turning it with a drill.
Click to expand...
QAOKMSK - Mark said:
10-4 on that, ok rubber o-ring on shaft, installed water tube correctly, closed up the motor ready to test. Side note, i have some grease at the power head that push out possibly during the overheat. Pic.
What do I need to look out for to make sure I still have a good seal?
Click to expand...
 
Back
Top