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Non-Resistor Spark Plugs & Boots = Problems

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Non-Resistor Spark Plugs & Boots = Problems

PostAuthor: chrismalm » Fri Jun 05, 2020 8:08 pm

I hope I'm not the last one to figure this out and it helps someone.
Long ago, I added "spark plug boot rebuild and resistor delete" to my Virago revival routine.
I also prefer Autolite AP63 spark plugs because they're platinum, help with cold starts, and they're available at any auto parts store. They have approximately 7.5k ohms resistance. I rebuild the plug boots and eliminate the resistor to achieve near-zero resistance in the boot. I have never had a problem with this setup.

I recently attached a spare engine to a dolly to test carburetors, ignition modules and regulators (see pics in my gallery). It had non-resistor plugs installed (NGK BP7ES) and I didn't give them a second thought. Despite meticulously rebuilding and bench-testing the carbs, the engine would idle ok, but would backfire with the slightest amount of throttle. It took a few more barks up wrong trees before I finally threw in a fresh pair of AP63s and it ran like a top afterwards.

My conclusion is : The ignition system in early Viragos requires resistance in the secondary circuit, either the plugs or the boots, or both.
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Re: Non-Resistor Spark Plugs & Boots = Problems

PostAuthor: Jake » Fri Jun 05, 2020 9:08 pm

Interesting. I never encountered a problem with AP63 and the stock boots with the resistor(2nd Gen). I will agree that the starts are better without the resistor in the boot and AP63.
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Re: Non-Resistor Spark Plugs & Boots = Problems

PostAuthor: chrismalm » Sat Jun 06, 2020 11:37 am

Good to know resistor plugs & boots works also. My theory has been updated.
Cheers !
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Re: Non-Resistor Spark Plugs & Boots = Problems

PostAuthor: Jake » Sat Jun 06, 2020 12:33 pm

I’ll have to see if I still have any NGKs and see if they work or not on the second gen without the boot resistor.
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Re: Non-Resistor Spark Plugs & Boots = Problems

PostAuthor: fitzy » Thu Jan 14, 2021 2:45 pm

An old (2005) post by cr_roger helps explain this a bit.

viewtopic.php?f=75&t=2841&p=15358&sid=d265b3c21c880b7c494f803ec0b74896#p15358

---

Could anyone please link me to a guide which explains the "spark plug boot rebuild and resistor delete" please? I am interested to see if there are recommenced plug boots and wires to do so with.
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Re: Non-Resistor Spark Plugs & Boots = Problems

PostAuthor: Jake » Thu Jan 14, 2021 3:53 pm

fitzy wrote:
Could anyone please link me to a guide which explains the "spark plug boot rebuild and resistor delete" please? I am interested to see if there are recommenced plug boots and wires to do so with.



http://faq.f650.com/FAQs/PlugCapsnCoils.htm
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Re: Non-Resistor Spark Plugs & Boots = Problems

PostAuthor: bstig60 » Wed Jan 27, 2021 11:44 am

I ran ap63 plugs with the stock boots in all my Virago's for years without any issues.
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Re: Non-Resistor Spark Plugs & Boots = Problems

PostAuthor: mark75 » Wed Jan 27, 2021 3:11 pm

fitzy wrote:An old (2005) post by cr_roger helps explain this a bit.

viewtopic.php?f=75&t=2841&p=15358&sid=d265b3c21c880b7c494f803ec0b74896#p15358

---

Could anyone please link me to a guide which explains the "spark plug boot rebuild and resistor delete" please? I am interested to see if there are recommenced plug boots and wires to do so with.



if you're going to change the cables, also ...

I replaced the spark plug cables with 7mm Accel "performance" ones, the ones with 'graphite' core, >>> https://www.holley.com/brands/accel/pro ... lug_wires/
but next time would go with copper-core ones. >>> viewtopic.php?f=5&t=7049

JMO: the copper ones "live well" longer in that application. graphite's fine in 'less exposed' situation.
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