I recently purchased two Johnson 70hp 3 Cylinder (1992?) engines. One was seized (to be kept for spares) and the other one started and revved smoothly on the sellers boat on the dry. However, when I installed the engine on my boat and took it to water, problems surfaced. It starts but as soon as it is put in gear, it dies or sometimes it revs up a little to about 1400 - 1600rpm and there it stuck. On dry land she revs like a banshee.
I stripped off the carburetors and took then totally apart and thoroughly cleaned all the jets, ports etc with carb cleaner and compressed air and everything is clean and open. Set the floats correctly and started the engine. Again, revved smoothly on the dry as before but the idling is a bit erratic - when left on a fast idle it will reduce rpm and dies and when tried to rev up just before it dies, it "hesitates" like it choking with too much air and then rev straight up.
Back in the water the same symptoms again. Timing is about 2 degrees at idle and 22 degrees at about 4000rpm - difficult to check correctly/accurately because strangely the timing marks are out by 180 degrees on the flywheel
Here is the history of engine:
1. Sat idle for about 1.5 years without being started.
2. Was used at coast and I stay inland at about 5000ft above sea level.
3. Compression on top two cylinders are 100-102psi and bottom piston measures about 92psi
4. Air screw turned out 1.5 turns.
Some friend suggest it is reed valve related, another suggested to change the fuel jets (which Im doubtful of, many guys I know use their boat at the coast regularly on holidays and inland without any ill effects or jet changes) and another point fingers to leaking crank casing seals.
I am really desperate. Can anybody please help pointing me in the right direction to get this engine sorted out.
I stripped off the carburetors and took then totally apart and thoroughly cleaned all the jets, ports etc with carb cleaner and compressed air and everything is clean and open. Set the floats correctly and started the engine. Again, revved smoothly on the dry as before but the idling is a bit erratic - when left on a fast idle it will reduce rpm and dies and when tried to rev up just before it dies, it "hesitates" like it choking with too much air and then rev straight up.
Back in the water the same symptoms again. Timing is about 2 degrees at idle and 22 degrees at about 4000rpm - difficult to check correctly/accurately because strangely the timing marks are out by 180 degrees on the flywheel
Here is the history of engine:
1. Sat idle for about 1.5 years without being started.
2. Was used at coast and I stay inland at about 5000ft above sea level.
3. Compression on top two cylinders are 100-102psi and bottom piston measures about 92psi
4. Air screw turned out 1.5 turns.
Some friend suggest it is reed valve related, another suggested to change the fuel jets (which Im doubtful of, many guys I know use their boat at the coast regularly on holidays and inland without any ill effects or jet changes) and another point fingers to leaking crank casing seals.
I am really desperate. Can anybody please help pointing me in the right direction to get this engine sorted out.
