Author Topic: Iridium plugs & Magneto  (Read 282 times)

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WayneBergman

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Iridium plugs & Magneto
« on: 16 June, 2021, 00:27:53 »
I have been reading with interest about these Iridium plugs.I have a 1952 BSA B33 and running a Mag/Dyno. Bike is hard to start but runs well once its going. Pretty sure I need a rebuild on my mag but in the mean time wondering if the Iridiem plugs will do anything for me in regards to easier to start.   From what I have read these plugs do not come in a non resistor version so not sure how this plays into using an Iridium plug with a mag.
Can anyone commment please on how a resistor type Iridium plug will work with a Mag?
Would the Iridium give a better spark even though it is not a NON RESISTOR type?
Thanks ........wayne

idie

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Re: Iridium plugs & Magneto
« Reply #1 on: 16 June, 2021, 09:23:07 »
Do not use resister plugs on a mag, the extra loading in trying to make a spark overloads the windings. If your mag is already a bit weak  a resistive plug will soon finish it off. Closing the plug gap by a few thou will help the mag.

JulianS

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Re: Iridium plugs & Magneto
« Reply #2 on: 16 June, 2021, 09:30:42 »
Used Denso iridium plugs on alloy head A10. Worked fine and seemed to burn cleaner with a good magneto BUT they did not last very long, less than 12 months before plug failure, 2 sets went that way and they are expensive to replace. They did not seem to like the magneto. Now back on Champions non resistors.

Our mag equipped bikes were fitted with resistor plug caps from 1953 by BSA.

A change in plug unlikely to compensate for a poor magneto.

idie

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Re: Iridium plugs & Magneto
« Reply #3 on: 16 June, 2021, 11:50:14 »
Plug caps used in the fifties were of low resistance especially made for magnetos roundabout 1000 ohms modern caps are around 5000 ohms. Carbon cored HT leads can be a 1000 ohms per foot. The days of 405 TV and AM radios are gone so our bikes don't cause the interference they used to do.

B Murphy

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Re: Iridium plugs & Magneto
« Reply #4 on: 16 June, 2021, 16:46:02 »
Iv'e got a Wassell Bantam trials that uses a DENSO IW16 Iridium Spark Plug, runs fantastic, no issues.

WayneBergman

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Re: Iridium plugs & Magneto
« Reply #5 on: 17 June, 2021, 04:13:47 »
Thanks guys, yes Idie I did try changing my gap from .020" to .012" and I would say the bike is running better. I also got some good advice to get the mag rebuilt when I can. I think the plan is to run the bike as is this Summer (bump starts for this year:)and in the fall send the mag out for a rebuild. I think I have spent enough on the bike for this season so next fall I will feel better about the mag overhaul.