Hi all,
I recently acquired an old 1976 Johnson 70HP and have been trying to learn how to repair it. Supposedly the previous owner used "engine starter" to get it running, though I can't say how often he did that or otherwise.
Problem:
The main issue it seems to be having is that it dies when it reaches slower RPMs, and sometimes dies when trying to give it more fuel by using the throttle linkage, or the throttle handle. However, when on the lake, if I use the primer (it has an electronic primer solenoid) once or twice right before increasing throttle, it'll take and rev up to speed and work fine. As soon as I decide to slow it down though, I have to be careful or it will eventually decrease in RPMs and die.
One thing I did try was spray a little Seafoam into the carbs a few times, and that seemed to resolve the idling problem at the time. So while the engine was burning through the Seafoam, it was fine.
Things I tried:
- Checked and replaced some fuel lines
- New OEM fuel pump
- New gas tank/connectors
- Rebuilt carbs with OEM parts and cleaned out every nook and cranny
- New spark plugs
- New ball/seat for control arm linkage
- Made sure the carbs all line up with each other and the "roller" lines up where it's supposed to on the plate (short line at idle, START line with warming lever fully engaged)
If I increase the idle screw enough, it'll stay running, but at a higher RPM than it's supposed to be at for idle.
Compression is the same across each cylinder.
NOTE: When I got the motor, the first and third carbs did NOT have a low speed orifice. I researched the engine model and purchased #30 orifices, but then found #2 carb has a #67 orifice. Finally, I researched the model number imprinted on the carbs and it looks like they are from a 1983 Johnson 75HP motor (they are all three the same part number).
Any thoughts/suggestions on what to test or look for? Seems like some fuel deliver issue
I recently acquired an old 1976 Johnson 70HP and have been trying to learn how to repair it. Supposedly the previous owner used "engine starter" to get it running, though I can't say how often he did that or otherwise.
Problem:
The main issue it seems to be having is that it dies when it reaches slower RPMs, and sometimes dies when trying to give it more fuel by using the throttle linkage, or the throttle handle. However, when on the lake, if I use the primer (it has an electronic primer solenoid) once or twice right before increasing throttle, it'll take and rev up to speed and work fine. As soon as I decide to slow it down though, I have to be careful or it will eventually decrease in RPMs and die.
One thing I did try was spray a little Seafoam into the carbs a few times, and that seemed to resolve the idling problem at the time. So while the engine was burning through the Seafoam, it was fine.
Things I tried:
- Checked and replaced some fuel lines
- New OEM fuel pump
- New gas tank/connectors
- Rebuilt carbs with OEM parts and cleaned out every nook and cranny
- New spark plugs
- New ball/seat for control arm linkage
- Made sure the carbs all line up with each other and the "roller" lines up where it's supposed to on the plate (short line at idle, START line with warming lever fully engaged)
If I increase the idle screw enough, it'll stay running, but at a higher RPM than it's supposed to be at for idle.
Compression is the same across each cylinder.
NOTE: When I got the motor, the first and third carbs did NOT have a low speed orifice. I researched the engine model and purchased #30 orifices, but then found #2 carb has a #67 orifice. Finally, I researched the model number imprinted on the carbs and it looks like they are from a 1983 Johnson 75HP motor (they are all three the same part number).
Any thoughts/suggestions on what to test or look for? Seems like some fuel deliver issue