Motorcycle Repair/Spark


Hi there, any help please? I have an '81 Yamaha single SR250 was running, now stopped, no spark at plug when turning over, yet with ignition on, if you toggle the kill switch on/off you get a great spark, checked the plse/trigger 680 ohms (Yam give 700 _+ 10%) tried bypass kill switch, taken off loom and replaced, checked contacts..If TCI was shot, could I still get spark in this way?



Hi John,

Many times people replace parts when all you need is some good
electronic cleaner spray like "DeOxit" or similar to remove the
oxidation from all the electric ignition components and connectors.

The connections may look okay but they do not make a good
electrical contact.

First make sure you have a load tested battery than has enough stamina
to keep up the spark while starting. Clean the cable connections
on the frame and the battery. Sand or file to reach new metal
if necessary.

Next, pull apart all the ignition components and spray the inside
of all the connectors. You might need to loosen the ignition coil
and make sure it is also grounded well to the frame.

Look inside the ignition connectors and see if any pins are bent or
pushed back inside and fix that.

See if the pulse trigger or pickup coil has a small voltage pulse
when you are cranking the engine. This would be very small
like 1 to 3 volts but should be noticable on a multimeter.

Try it without the spark plug cap or use a new cap.

Check the starting system for excess current draw or
poor connections on the relay or cables to the starter
and battery.

If you have a steady pulse voltage then check the ignition unit
connectors for corrosion or bent pins.

NOTE: I believe the power to your coil and ignition unit
comes from the engine stop or kill switch so
check for power to your coil with the stop switch on.

You can connect a battery charger to see if you have insufficient
battery stamina. the ignition units will switch off if they do not
receive enough current so anything like a weak connection
or low battery can affect them.

There could be loose solder joints in the ignition module
that could be repaired possibly unless you can find a
used one or a aftermarket replacement.

I would not change the ignition module until a full
connector cleaning was done and if the pulse coil
seems to be producing a regular voltage pulse.

Your coil sounds okay but you can even connect it to a
battery and see if it sparks consistently when
voltage is applied on and off quickly.
Spark should jump about 5 or 6mm or 1/4"

On bikes this age it is about 90 per cent of the time corrosion
and poor connectors that causes these problems.
The battery is unable to provide enough current over bad connections
to keep the ignition module active so it switches off to protect itself.
The starting system can draw so much power away that the module
quickly switches off.

Last resort is usually replacing the ignition module or pulse trigger
if it shows no or weak output.

Hope this made some sense,


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Wayne S.


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


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

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