FishMan001
Cadet
- Joined
- May 2, 2021
- Messages
- 26
Hi,
Firstly, sorry for the long post !!!
About 6 months ago I bought a 2004 Yamaha 70B outboard (same as the 50G and 60F) from a guy who had owned it from new.
It had been sat in his shed for over a year because it was "unreliable" - It didn't start very easily and stopped giving enough power.
The tacho shows the hours as 316 (and is genuine).
My problem !
On the boat and in the water, it starts easily and appears to idle well (800RPM). It will rev to 5000+ RPM in neutral. When I take it out on the sea, it will slowly get to 3000 RPM (5 secs), and that's it. Once, it bust into life and went upto about 5000, but then within a minute, it was back to 3000. When it's running at 3000, it seems "lazy" and will vary from 2800-3100 over the course of about 5 seconds, and sounds as if it's running on 2 cylinders.
I am using fresh petrol, no ethonol or additives.
I took off the air box, and the carb throttles were all fully open when running.
Pulling off each spark plug top causes a similar reduction in revs for each one.
Blocking each carb intake causes a similar drop in RPM for each one.
I stopped and pulled out the plugs, and they were all black and wet. So I assumed fuel/carb problems.
I thought it might be the Primestart, so at a fast idle, I switched the red emergency lever to "ON" to see if the fuel was coming from there, and it stalled.
I pulled apart the emergency start (yellow wire) connector under the CDI, and the revs increased.
I pulled the carbs off again, cleaned them out again (they were spotless), and checked the float height (spot on 14mm for all of them).
The things I have done so far are:
All fuel lines blown through with carb cleaner
Air box cleaned (and clear)
Cowling hood air intake cleaned (and clear)
New plugs
New fuel filter
New fuel pump
New thermostat
Drained 2 stroke oil reservoir, cleaned and refilled
Primed the oil lines
Checked oil pump linkage
Stripped the carbs, cleaned with carb cleaner and blew out jets
New needle valves and holders
Set idle screws to just over 1 turn out
Adjusted carb linkages and stops
Pulled reed valves - looked clean and couldn't see any light through them
Adjusted CDI linkages to spec
Adjusted timing to 7' ATDC for idle, and 20' BTDC for full throttle, with timing light
Checked the coils primary and secondary resistances were in spec
Pulled apart all electrical connections (including earths), cleaned and put back
Checked oil and temp sensors for correct operation and alarm
As all 3 plugs are black and wet, I assume it must be something common to all cylinders, but I am now at a loss.
Please can anyone give me either any more tests to try, or, if you've had similar problems, what the problem may be.
Thanks for any help !
Paul
Firstly, sorry for the long post !!!
About 6 months ago I bought a 2004 Yamaha 70B outboard (same as the 50G and 60F) from a guy who had owned it from new.
It had been sat in his shed for over a year because it was "unreliable" - It didn't start very easily and stopped giving enough power.
The tacho shows the hours as 316 (and is genuine).
My problem !
On the boat and in the water, it starts easily and appears to idle well (800RPM). It will rev to 5000+ RPM in neutral. When I take it out on the sea, it will slowly get to 3000 RPM (5 secs), and that's it. Once, it bust into life and went upto about 5000, but then within a minute, it was back to 3000. When it's running at 3000, it seems "lazy" and will vary from 2800-3100 over the course of about 5 seconds, and sounds as if it's running on 2 cylinders.
I am using fresh petrol, no ethonol or additives.
I took off the air box, and the carb throttles were all fully open when running.
Pulling off each spark plug top causes a similar reduction in revs for each one.
Blocking each carb intake causes a similar drop in RPM for each one.
I stopped and pulled out the plugs, and they were all black and wet. So I assumed fuel/carb problems.
I thought it might be the Primestart, so at a fast idle, I switched the red emergency lever to "ON" to see if the fuel was coming from there, and it stalled.
I pulled apart the emergency start (yellow wire) connector under the CDI, and the revs increased.
I pulled the carbs off again, cleaned them out again (they were spotless), and checked the float height (spot on 14mm for all of them).
The things I have done so far are:
All fuel lines blown through with carb cleaner
Air box cleaned (and clear)
Cowling hood air intake cleaned (and clear)
New plugs
New fuel filter
New fuel pump
New thermostat
Drained 2 stroke oil reservoir, cleaned and refilled
Primed the oil lines
Checked oil pump linkage
Stripped the carbs, cleaned with carb cleaner and blew out jets
New needle valves and holders
Set idle screws to just over 1 turn out
Adjusted carb linkages and stops
Pulled reed valves - looked clean and couldn't see any light through them
Adjusted CDI linkages to spec
Adjusted timing to 7' ATDC for idle, and 20' BTDC for full throttle, with timing light
Checked the coils primary and secondary resistances were in spec
Pulled apart all electrical connections (including earths), cleaned and put back
Checked oil and temp sensors for correct operation and alarm
As all 3 plugs are black and wet, I assume it must be something common to all cylinders, but I am now at a loss.
Please can anyone give me either any more tests to try, or, if you've had similar problems, what the problem may be.
Thanks for any help !
Paul
