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Proper spark plugs for 75/5 with electronic ignition

Bruce Suehr
(@bruce-suehr)
Active Member

Hello all, I'm am working towards an initial startup on a 73 , R75/5. Carbs are completely rebuilt, tank cleaned and sealed, petcocks rebuilt. I bought the bike with a dyna111 ignition on it. I put new wires on it with 5k ohm caps. I do not know what plugs I should use on the bike. I also would like advice on where to acquire the gasket that goes on the bottom of the petcocks ( carb side), or a suitable substitute. I very much appreciate your help. Bruce

Quote
Topic starter Posted : 05/13/2022 17:52
Richard Whatley
(@wobbly)
Member Moderator

I have been using NGK BP7ES for years. Unfortunately, NGK ceased production of non-resistor type plugs not too long ago. You may still find some in stock at local auto parts stores.

You definitely want the "protruded tip" design. And 7 is almost a universal heat range for all air-cooled engines.

If you are forced to convert over to "resistor type" plugs the number would become BP7RES, but I'm not sure if you then need to remove the resistor caps and replace them with non-resistor caps when you change the plug. I haven't gotten that far.

[color=blue]Don't hide 'em, Ride 'em !!
#15150[/color]

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Posted : 05/15/2022 16:17
Bruce Suehr
(@bruce-suehr)
Active Member
  1. Thanks Richard. Found some Bosch supers, non resistor in a 6 heat range. Sound good?  
ReplyQuote
Topic starter Posted : 05/15/2022 19:56
Richard Whatley
(@wobbly)
Member Moderator
Posted by: @bruce-suehr
  1. Thanks Richard. Found some Bosch supers, non resistor in a 6 heat range. Sound good?  

I've never been a "Bosch guy". The heat range numbering system is completely the invention of the plug maker. NGK plugs get colder when the numbers get higher; with Champions it goes the opposite direction and gets hotter. I have no idea which way Bosch plugs go.

Books can be wrong, especially on a bike with 10 previous owners. You'll want to have a small amount of beige or tan coloration on the porcelain center after several miles of constant throttle while riding at cruising speeds between 55 to 70mph. On new plugs this color may not appear for 25+ miles.

Tip: Whenever fitting or re-fitting ANY steel threaded spark plug into an aluminum cylinder head it is always a good idea to apply grease, motor oil, or some form of Never-Seize. Any lubricant is 100% better than nothing. 

Hope this helps.

[color=blue]Don't hide 'em, Ride 'em !!
#15150[/color]

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Posted : 05/17/2022 14:29
Bruce Suehr
(@bruce-suehr)
Active Member

Thank you Richard. Appreciate very much your replies. Used copper antisieze on them. I guess I'll have to focus on diagnosing whether I have a valve recession issue at this point in the journey. I guess Ted Porter is no longer doing head work so I'll need to find an alternative ( or buy his equipment and get trained on how to use it and take over head rebuild for the airhead community). Best regards, Bruce

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Topic starter Posted : 05/19/2022 05:27

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