Gimbo
Cadet
- Joined
- Jul 14, 2011
- Messages
- 13
I have this old Johnson 4Hp from 1973. Same year of birth as my wife and equally hard to start 
However with a few minor hickups, it has always started, and when it did it was running fine until I stopped it. And then started again, with a pull or two.
Until this summer season, that did not start until August, as I was replacing the SIB I had it on, with a glassfiber boat.
Anyway the motor had not been used for a couple of years at this point.
Had one trip where it behaved more or less like normal. Except that I had to give it a lot more throttle to make it start. ANd it would only run at all with the slow setting sett all the way to lean, and the fast knob (under) all the way to the right.
But then it ran okay. But always felt that the motor had more to give when it came to speed.
It pushed my 14 foot glassfiber rowing boat to 4,8 knots at full throttle. I ran at full thiorttle for ten minutes one day and the thing stopped on me. Manged to srat it again, after a cool down, and it rain fine.
Next time I used the boat however, it would run for a while , then lose RPM and stop.
I am afraid I might have overheated it.
Now season is over so I took home the motor to look it over. And perhaps rebuild the whole thing just for fun (and to learn it)
Carb
Started with the carb. There was no gunk in it. But it looks like there was some condensation in it. That may expalin the loss of rpm and then stop?
Cleaned it it with carb cleaner and air in a can. But noticed some of the gaskets where brittle so ordered a gasket kit, to replace all of them. So just put it back together to avoid losing parts, and set it aside.
Fuel pump:
So far only inspected the filter in the fuel pump, looks clean, but will rebuild that just to know when it was last done. I have not touched it in the 8 years I have had the motor. But it has only been used 3-4 times every summer....
Gas lines looks pristine, on the outside. But wiull replace those too.
Spark plugs:
Both are sparking, and smelled of gasoline when I pulled them out.
However 3 years ago, I managed to mess up the upper plug threads. And had to make new threads and use an insert.
So maybe I will replace the cylinder head just because of that?
Cylinder head
It looked like the cylinder gasket was leaking. So I pulled the cylinder head off to have a look. Turned out that
3 out of 4 cylinder head bolts where quite loose They turned without any initial resistance at all.
So I do not think the compression has been what it should be.
Could this be a reason for it starting, and then as it gets warm it drops RMP, and then stop?
I have not looked closely at the cylinder head yet. But the cylinder walls looks nice and shiny and clean.
Thinking of going deep in and look at the cylinders as well. WHat do you think?
WIll probably replace the cylinder head and definately the gasket.
----------
Any advice, and tips about things to look at, check will be deeply appreciated :-D
However with a few minor hickups, it has always started, and when it did it was running fine until I stopped it. And then started again, with a pull or two.
Until this summer season, that did not start until August, as I was replacing the SIB I had it on, with a glassfiber boat.
Anyway the motor had not been used for a couple of years at this point.
Had one trip where it behaved more or less like normal. Except that I had to give it a lot more throttle to make it start. ANd it would only run at all with the slow setting sett all the way to lean, and the fast knob (under) all the way to the right.
But then it ran okay. But always felt that the motor had more to give when it came to speed.
It pushed my 14 foot glassfiber rowing boat to 4,8 knots at full throttle. I ran at full thiorttle for ten minutes one day and the thing stopped on me. Manged to srat it again, after a cool down, and it rain fine.
Next time I used the boat however, it would run for a while , then lose RPM and stop.
I am afraid I might have overheated it.
Now season is over so I took home the motor to look it over. And perhaps rebuild the whole thing just for fun (and to learn it)
Carb
Started with the carb. There was no gunk in it. But it looks like there was some condensation in it. That may expalin the loss of rpm and then stop?
Cleaned it it with carb cleaner and air in a can. But noticed some of the gaskets where brittle so ordered a gasket kit, to replace all of them. So just put it back together to avoid losing parts, and set it aside.
Fuel pump:
So far only inspected the filter in the fuel pump, looks clean, but will rebuild that just to know when it was last done. I have not touched it in the 8 years I have had the motor. But it has only been used 3-4 times every summer....
Gas lines looks pristine, on the outside. But wiull replace those too.
Spark plugs:
Both are sparking, and smelled of gasoline when I pulled them out.
However 3 years ago, I managed to mess up the upper plug threads. And had to make new threads and use an insert.
So maybe I will replace the cylinder head just because of that?
Cylinder head
It looked like the cylinder gasket was leaking. So I pulled the cylinder head off to have a look. Turned out that
3 out of 4 cylinder head bolts where quite loose They turned without any initial resistance at all.
So I do not think the compression has been what it should be.
Could this be a reason for it starting, and then as it gets warm it drops RMP, and then stop?
I have not looked closely at the cylinder head yet. But the cylinder walls looks nice and shiny and clean.
Thinking of going deep in and look at the cylinders as well. WHat do you think?
WIll probably replace the cylinder head and definately the gasket.
----------
Any advice, and tips about things to look at, check will be deeply appreciated :-D
