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Motorcycle Repair/CB450SC 1982, no spark in cold


I have a CB450SC imported from the states. All runs fine until you try to start it on a cold morning. No spark at all when cranking but will fire-up if push-started. Then it will have no problems running and will start easily for the rest of the day after. Carbs are clean, coils, leads, caps and plugs are new. The frame is well grounded to the battery terminal.

I have checked all wire resistances at the stator connectors as given in the manual and they are all close to spec. (see below):

Cables   Manual  Ω   My Generator Ω
Grn-Wht     315-385       286
Blu-Wht     77-95          77
Grn-Brn     76-92          87
Grn-LtBlu 95-116   103
Grn-Pink  126-154   121
Yel-Yel   < 1          0.9

I know the 'pulser coil' is reported to be a notorious culprit in these, but do not know which coil that refers to. Is it the coil mounted OUTSIDE the flywheel cover that is driven by a small round magnet? or is it inside, part of the stator?

If it is the external coil, is there anything I could do to improve the pulse? - it is nearly impossible to locate a new stator + loom for these bikes.

Many Thanks,

Hi Tony,

The fact that your bike starts when warm indicates it has too much
current draw when cold. This might mean the starter needs
cleaning up or new brushes. Also the connectors for the whole starting system
should be cleaned with a good electronic spray cleaner like
deoxit or MG chemical cleaner.

Next, I would get the battery charged and load tested as any weakness
there will be a problem. Even a cheap or low amp battery may not
provide enough juice when cold.

If the pulse coil were bad it probably would not run well when warm.
The pulse coil has blue/yellow and green wires on the connector
under the seat. It should read about 50-170 ohms.

When you push start it the battery has enough juice to power
everything. The starter is either drawing too much power away
from the ignition or you need a stronger battery.
That would be my guess anyway.

Also check if your charging system is working well.
Have you ever checked if it has spark when cold if you kickstart it?

PS: The pulse generator coil is the small separate outer coil
not inside the stator coil.

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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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