Dunaruna
Admiral
- Joined
- May 2, 2003
- Messages
- 6,027
1992 70hp yamaha 2 stroke.
Recent history -
Purchased a few months ago. In driveway (in a tub), spark is o/k, comps are excellent. Starts and runs well but only with fuel bypass switch on 'emergency' , will not run with switch off. Rebuild all 3 carbs and enriching fuel pump diaphragm. Replace electrothermal valve. It now starts and runs with switch 'off'. In fact, when cold, it starts like an EFI (almost 'turn key start').
Test oil injection (o/k), test temp sensor (o/k), inspect timing sync (no adjustment needed). Inspect reed valves (o/k). Replace spark plugs. Clean fuel filter (not dirty), replace fuel bulb and hoses, clean out fuel tank (not dirty), replace fuel click connectors, inspect fuel tank breather (not blocked).
Take boat to lake for test run. It is grossly underpowered, will not plane out although it sounds o/k, no missfire or splutter. It is not ventilating. The prop and hub are in excellent condition. Test coil resistance, found 2 coils open circuit on the secondary side, on closer inspection found badly corroded plug wires (inside the outer covering). Replace all 3 coils.
Immediate results, jumps out of the water and planes out at 45 MPH at 3/4 throttle, Sweet!
Problem -
With every bump or wave, it missfires and faulters, as the water calms down it resumes normal revolutions. This occurs at any throttle position including fast idle. My first thought was float level so off with the carbs (again). Cannot fault float level, cannot fault any part of the carb circuits. All is clean and within specifications. Bowls are full and fuel pressure is good. This problem does not occur if I adjust the trim up and down, it only occurs when the water is rough.
I need a fresh pair of eyes to point me in the right direction, any ideas?
Recent history -
Purchased a few months ago. In driveway (in a tub), spark is o/k, comps are excellent. Starts and runs well but only with fuel bypass switch on 'emergency' , will not run with switch off. Rebuild all 3 carbs and enriching fuel pump diaphragm. Replace electrothermal valve. It now starts and runs with switch 'off'. In fact, when cold, it starts like an EFI (almost 'turn key start').
Test oil injection (o/k), test temp sensor (o/k), inspect timing sync (no adjustment needed). Inspect reed valves (o/k). Replace spark plugs. Clean fuel filter (not dirty), replace fuel bulb and hoses, clean out fuel tank (not dirty), replace fuel click connectors, inspect fuel tank breather (not blocked).
Take boat to lake for test run. It is grossly underpowered, will not plane out although it sounds o/k, no missfire or splutter. It is not ventilating. The prop and hub are in excellent condition. Test coil resistance, found 2 coils open circuit on the secondary side, on closer inspection found badly corroded plug wires (inside the outer covering). Replace all 3 coils.
Immediate results, jumps out of the water and planes out at 45 MPH at 3/4 throttle, Sweet!
Problem -
With every bump or wave, it missfires and faulters, as the water calms down it resumes normal revolutions. This occurs at any throttle position including fast idle. My first thought was float level so off with the carbs (again). Cannot fault float level, cannot fault any part of the carb circuits. All is clean and within specifications. Bowls are full and fuel pressure is good. This problem does not occur if I adjust the trim up and down, it only occurs when the water is rough.
I need a fresh pair of eyes to point me in the right direction, any ideas?