LCGB Forums

Hi All.
Bit of advice needed please, Popped out on my first ride of the year last week and scooter died on me. Was using a denso resistor plug that appeared to fail. Could it be an unlucky one or should I not be using a resistor spark plug, does it make any difference at all running a standard scooter LI150S all original 6v points etc
..dropped in a spare standard NGK one and it fired up first time. The denso one hadn't done that many miles that's why I'm wondering if it's not intended.
Thanks in advance.

If your engine has a plug cap with an integral resistor then you need an unsuppressed plug or visa versa. If you have a suppressed cap and a suppressed plug then this will severely impact on the spark voltage leading to a fouled plug.
An unsupressed cap with an unsuppressed plug will bug nearby radios and send a SIP speedo doolali.
Unscrew the plug cap from the lead and use a multimeter to measure the resistance across the input / output. A suppressed cap will usually show around 5000 ohms. An unsupressed cap will show near zero ohms.
Do the same with your spark plug to confirm that also.

Thanks for your reply. That all makes sense to me, explains why the plug had a week spark, I'll grab my multimeter and check the cap out as you suggest.
Another piece of knowledge in my locker, thank you FnF

I’m not wishing to contradict, but despite OEM plug caps being suppressed, a points based ignition should not be suppressed according to tuners such as Bell, who also advocates fine wire plugs which are worth having if not paying a ridiculous premium IMO.

Suppression was applied/legislated upon vehicles to avoid interference with televisions etc but that no longer appears to be a problem.

AF Rayspeed & probably many other dealers sell excellent Champion non suppressed plug caps.

To clarify:- Inductive ignitions should have 1K ohm of suppression and capacitive discharge 5K ohm.

Warkton Tornado No.1 wrote:I’m not wishing to contradict, but despite OEM plug caps being suppressed, a points based ignition should not be suppressed according to tuners such as Bell, who also advocates fine wire plugs which are worth having if not paying a ridiculous premium IMO.

Suppression was applied/legislated upon vehicles to avoid interference with televisions etc but that no longer appears to be a problem.

AF Rayspeed & probably many other dealers sell excellent Champion non suppressed plug caps.

Yip, I use both plug n cap in Non resistance flavour just for a better spark