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Discussion Starter · #1 ·
I have a yamaha 4 stroke. Is the ingition powered by a magneto or the alternator via the battery?

Thanks
 

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ignition key is powered from your battery, turning the key then sends power to the starter. alternator's and magneto's depending on the motor do not come into play until a motor starts to spin
 

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That is correct Scott,

the battery supplys voltage to the switched B+ and a ground, which in turn supplys voltage to the main power relay on the engine, which in turn supplys power to the starter relay the fuel pump relayand the ign relay. when the engine starts spinning the stator supplys AC voltage to be converted to DC voltage to power the electronics on the engine.

hope this isnt confusing. what seems to be the problem with your engine..
 

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Discussion Starter · #4 ·
Thanks. What i was trying to determine was if the engine is self sustaining after it is running, even if the battery or alternator fails. In airplanes, there isa magneto that powers the iignition system (spark plugs), so that the engine will not fail in the event of an electrical failure.

The reason i ask is one of my motors failed the other day. It ran fine the rest of the day after we switched to the other battery, and i was trying to isolate the problem to electrical or fuel.

Thanks
 

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A quick way to tell if the battery is being charged is to take a voltage reading before starting the engine. Then observe the voltage meter after starting. There should be an increase in the voltage after starting the engine. If the voltage drops or stays the same after starting you have a problem somewhere.
 

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Yes a dead battery will stop a fuel injected 4 stroke from running, it requires a 12v supply to power up the main and fuel pump relays.

a carb engine will remain running due to cdi,
 

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Sequoiha Yes a dead battery will stop a fuel injected 4 stroke from running, it requires a 12v supply to power up the main and fuel pump relays.
a carb engine will remain running due to cdi,--------------------------------------------------------------------------------------------------------------------------------------------------------------------I wonder if that implies thatmy 02' Yamaha 100 hp 4- stroke carbureted engine will continue running with the battery disconnected ?
 

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Emerald Ghost (13/05/2010)Sequoiha Yes a dead battery will stop a fuel injected 4 stroke from running, it requires a 12v supply to power up the main and fuel pump relays.
a carb engine will remain running due to cdi,--------------------------------------------------------------------------------------------------------------------------------------------------------------------I wonder if that implies thatmy 02' Yamaha 100 hp 4- stroke carbureted engine will continue running with the battery disconnected ?
Test it out and let us know.
 

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Emerald Ghost (13/05/2010)Sequoiha Yes a dead battery will stop a fuel injected 4 stroke from running, it requires a 12v supply to power up the main and fuel pump relays.
a carb engine will remain running due to cdi,--------------------------------------------------------------------------------------------------------------------------------------------------------------------I wonder if that implies thatmy 02' Yamaha 100 hp 4- stroke carbureted engine will continue running with the battery disconnected ?
I havnt tried it yet but it should keep running,
 
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