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Motorcycle Repair/83 honda magna 750

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Question
I am having a problem with spark on one coil. it has power to it and it sparks until the bike warms up. it is a good coil I have checked it, there is power to everything. Help Please!!!

Answer

Hi Jason,

There are a few things that can cause spark problems.

-weak battery
-corrosion in the wire connectors.
-ignition coil breaking down when hot.
-ignition pulse generator coil breaking down when hot.
-ignitor or control unit faulty.

Sometimes you can swap the wire connectors or the coils
and control ignitors themselves to see if the
problem changes to the other set of spark plugs.
This will tell you if the coil is bad or the ignitor or
the pulse generators.

If you swap certain parts to the running cylinders
and it causes the spark to quit again then you have
narrowed the cause down to a certain component.

The ohms meter tests do not always identify a bad component.
Often the parts will malfunction when they are heated up.

If you are convinced the coil is not failing when hot
then the next component to check would be the
pulse generator(s) under the right side clutch cover.

These generally read about 480 ohms on older Magnas
Wires are white/yellow to yellow
and white/blue to blue

If the ohms reading changes drastically when hot then
there may be a problem there.

The last resort is always the ignitor boxes themselves
but you may be able to swap them to see if one is faulty or not.

The coils grounding circuits are just as important as the power side
so clean up connectors with electronic spray cleaner to remove
any corrosion.

The ignitor boxes can shut down if the battery voltage is too low
and the spark plug caps may have resistors in them that can fail.

If you have a timing light that can show you if the spark is working
or not at various temperatures and speeds.

Luck to you on finding the spark culprit.


Wayne S
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Motorcycle Repair

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Wayne S.

Expertise

Licensed Motorcycle Mechanic, Knowledge of motorcycles from 1960 up, Japanese, British and most other brand motorcycle repairs.

Experience

Worked for Yamaha, Honda, Suzuki, Kawasaki British: Triumph, Norton, BSA Other: Most Scooters and Mo-Peds

Publications
Canadian Motorcycling magazine article

Education/Credentials
Licensed Motorcycle Mechanic

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