Suzuki T250 motorbike (1972) - Spark plug cap - resistors

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Sat 11 Feb 2023 10:40
Suzuki T250 motorbike (1972) - Spark plug cap - resistors - rustonboy

Please does anyone know whether the spark plug caps on this model should have a resistor? The coils are the originals and tested fine, but new spark plug caps are needed, so getting the right ones will obviously affect the strength of the spark. Many thanks :-)

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Sun 12 Feb 2023 09:20
Suzuki T250 motorbike (1972) - Spark plug cap - resistors - Surreydriver

I owned several bikes in that era and do not recall resistor caps being an issue. I thought resistance was part of the spark plug specification if required. I would post this on a Suzuki bike forum where you are much more likely to get an informed response with this and any other issues you may encounter.

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Sun 12 Feb 2023 16:26
Suzuki T250 motorbike (1972) - Spark plug cap - resistors - craig-pd130

The only reason for the resistors in the caps originally was to suppress TV interference from the HT voltage firing the plugs. Resistors are not necessary as far as the ignition system is concerned.

For what it's worth, I ran my Suzi GT380 on B8EIX iridium spark plugs (they never foul and never need re-gapping once installed). Those do have a built-in 5K ohm resistor, so I used NGK non-resistor plug caps. This was with the factory points ignition set-up.

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Wed 15 Feb 2023 18:21
Suzuki T250 motorbike (1972) - Spark plug cap - resistors - rustonboy

Many thanks for those suggestions - I think we will will probably run without resistors and enjoy the best spark possible :-)

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Thu 16 Feb 2023 09:58
Suzuki T250 motorbike (1972) - Spark plug cap - resistors - craig-pd130

Many thanks for those suggestions - I think we will will probably run without resistors and enjoy the best spark possible :-)

One thing to note: you might find that the factory recommended setting for ignition timing is a bit too far advanced for today's fuels.

Suzuki's recommended setting was quite advanced to help give the engine a bit more mid-range torque, but can risk detonation and burning pistons.

I would strongly recommend borrowing / buying a dial gauge and retarding the timing by 0.25mm or so. My GT380 'pinked' audibly at the factory setting, but when retarded by 0.3mm it ran sweet as a nut.

If you can't easily get a dial gauge, retard the ignition by a couple of degrees of crank rotation by observing the factory marks on the flywheel.

Also, I would very strongly recommend using Super Unleaded at all times, the lower ethanol content is much kinder to all the carb and inlet rubbers.

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Thu 16 Feb 2023 12:52
Suzuki T250 motorbike (1972) - Spark plug cap - resistors - rustonboy

That's a great tip - nothing like experience to avoid the pitfalls - many thanks indeed :-)

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