Logo
FULL SITE MENU

1978 Johnson 35 suddenly unable to idle

J

JohnBZ

New member
I picked up the motor this spring and had issues with flooding. I replaced the fuel pump and rebuilt the carburetor. All summer long the motor ran great. Last week I had issues with the motor being difficult to cold start. Once it fired up it ran fine. Subsequent restarts were easy. The most recent time out the motor started after several minutes of attempting and idled fine. After 5 minutes of running at no wake speed the motor suddenly quit. It would restart but will not idle. It will run at higher rpm but will not sustain an idle. Partially choking helped slightly but it will still not sustain an idle. I tried adjusting the idle screw back to 1.25 turn out and it had no effect. Introed various settings with the idle screw. I checked all the linkages and found nothing amiss. I replaced the plugs, which didnt help. In desperation i pulled the carburetor and gave it a thorough cleaning and rebuilt it again. I replaced the float, needle and seat. I set the float per the instructions. That had no effect. I checked the spark with an adjustable tester. Spark is strong and would easily jump a .25" gap on both cylinders. I replaced the fuel pump gaskets. I also pulled the fuel line off the carb. Pulling the recoil was enough to pump fuel. I found when the motor dies out the plugs are wet. During testing the plugs quickly become covered in carbon deposits. Any ideas of what to do from here ?
 
There is no mention of a simple compression test.-----That is step # 1 in trouble shooting.-----You did replace the water pump impeller when you bought this motor I hope.-----You have inspected / tested the thermostat ?
 
I replaced the impeller immediately when i bought it. And immediately changed the lower unit oil. The thermostat is operating fine. I have not retested compression since i purchased the motor but it was good when i purchased it. I dont remember the exact numbers but both cylinders were over 120.
 
JohnBZ said:
First rebuild was with a sierra kit. Second time was an OMC kit.
Click to expand...

I rebuilt the carb on my 4W75A with an off brand kit and the gasket between the top and bottom
of the carb promptly dissolved sending bits all through the carb. Still have some bits in my low speed jets.

Lesson learned.
 
Everything looked good with the gaskets i pulled out when doing the second rebuild. There didnt seem to be any big difference in quality between the sierra and OMC rebuild kits. I am going to pick up a compression tester and check again. I borrowed one when i bought the motor. Since ive got 3 older omc motors it probably not a bad idea to have one around.
 
Back
Top