I have a 1986 Yamaha 70 hp, model 70ETLJ, 3 cylinder 2-stroke outboard. It started misfiring mid-summer after 30 or more minutes of perfect running. On subsequent trips the misfire started progressively sooner. Misfire now starts after about 10-15 minutes at operating temperature.
I ran it on the water this past week under load and by pulling one plug wire at a time found that the misfire is on cylinder 3. Switched coils around and made sure to correctly switch primary leads from cdi unit. Misfire still on cylinder 3 Switched spark plugs around. No change; misfire is on 3. The only difference between No. 3 plug wire connected and disconnected is that it "tries" to come out of the hole with the wire on the plug, with intermittent firing on No. 3 cylinder, but spark on No. 3 soon breaks down or goes away.
Here's what I've done:
All carbs cleaned and good fuel filter. New fuel tank and lines. New NGK plugs, correct model.
Checked compression when cold and got 120 psi +/- 5 psi on all cylinders.
Checked spark when cold and got well over 15,000 volts at each plug wire.
Replaced CDI unit with identical unit.
Removed all three coils and checked primary and secondary coil resistance both cool and when heated up. All are on spec, based on Yamaha manual.
I checked the triggers' resistance and got 130-135 ohm on all three (black to white/green, black to white/black, black to white/red). This is right to spec.
Checked the triggers' voltage when cranking engine, and got 0.6 volts AC. SPEC. for triggers with DVA is 2.5 volts.
QUESTION: Does the fact that I used a non-DVA meter but watched the readings carefully and they never went above 0.6 volts mean my reading is likely accurate, or do I absolutely need a DVA meter to get correct reading?
I checked stator resistance, brown wire to black and got 160 ohms, which is right in specified range. HOWEVER, the stator cranked only about 40 volts AC and the specified voltage is 140.. Again, is this reading taken with a digital non DVA meter, but carefullyl observed not to ever read above 40 volts in 5-10 seconds of cranking, accurate?
My gut is telling me that the stator-trigger assembly is at fault. But after chasing a CDI solution, I want to have solid advice from more experienced troubleshooters before buying more electronic parts. Yamaha ignition parts are reputed to be really reliable so I don't want to buy more of what I don't need.
Should I pull the flywheel and see what the stator assembly looks like? Any chance that a fault giving the above symptoms would be visible?
Since this motor starts right up and runs great for 15 minutes before the problem, am I right to believe that it is not a fuel system issue? Is there any other area besides ignition that it could be?
If you've worked through problems like mine, I'd appreciate your advice. Thanks.
I ran it on the water this past week under load and by pulling one plug wire at a time found that the misfire is on cylinder 3. Switched coils around and made sure to correctly switch primary leads from cdi unit. Misfire still on cylinder 3 Switched spark plugs around. No change; misfire is on 3. The only difference between No. 3 plug wire connected and disconnected is that it "tries" to come out of the hole with the wire on the plug, with intermittent firing on No. 3 cylinder, but spark on No. 3 soon breaks down or goes away.
Here's what I've done:
All carbs cleaned and good fuel filter. New fuel tank and lines. New NGK plugs, correct model.
Checked compression when cold and got 120 psi +/- 5 psi on all cylinders.
Checked spark when cold and got well over 15,000 volts at each plug wire.
Replaced CDI unit with identical unit.
Removed all three coils and checked primary and secondary coil resistance both cool and when heated up. All are on spec, based on Yamaha manual.
I checked the triggers' resistance and got 130-135 ohm on all three (black to white/green, black to white/black, black to white/red). This is right to spec.
Checked the triggers' voltage when cranking engine, and got 0.6 volts AC. SPEC. for triggers with DVA is 2.5 volts.
QUESTION: Does the fact that I used a non-DVA meter but watched the readings carefully and they never went above 0.6 volts mean my reading is likely accurate, or do I absolutely need a DVA meter to get correct reading?
I checked stator resistance, brown wire to black and got 160 ohms, which is right in specified range. HOWEVER, the stator cranked only about 40 volts AC and the specified voltage is 140.. Again, is this reading taken with a digital non DVA meter, but carefullyl observed not to ever read above 40 volts in 5-10 seconds of cranking, accurate?
My gut is telling me that the stator-trigger assembly is at fault. But after chasing a CDI solution, I want to have solid advice from more experienced troubleshooters before buying more electronic parts. Yamaha ignition parts are reputed to be really reliable so I don't want to buy more of what I don't need.
Should I pull the flywheel and see what the stator assembly looks like? Any chance that a fault giving the above symptoms would be visible?
Since this motor starts right up and runs great for 15 minutes before the problem, am I right to believe that it is not a fuel system issue? Is there any other area besides ignition that it could be?
If you've worked through problems like mine, I'd appreciate your advice. Thanks.
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