Board index Flathead Power-Technical Questions, Answers, and Suggestions K-Models Spark plugs

Spark plugs

Moderators: Curt!, Pa

Post Mon Nov 13, 2006 3:55 pm

Posts: 55
Location: west coast
What is a good plug, made currently, for K and KH models ?

Post Wed Nov 15, 2006 1:41 pm

Posts: 149
Location: calif
hi NGK. i would start with a 7 heat range go from there

Post Wed Nov 22, 2006 7:15 pm

Posts: 240
Location: Kirkland, WA, USA

I use B7ES or B8ES NGK. I used to use Champion NC4, but they are no longer available. Barry55KH

Post Thu Nov 23, 2006 12:03 pm

Posts: 54
Pay attention that the NGK B7ES are long reach plugs that only fit if you happen to have KR heads installed.
For my stock KH NGK B6HS work well for in town and 55 mph cruising. They are equivalent to HD #3 which is what the factory recommended. For high speed operation B7HS would be your choice, equivalent to HD #4, again what the factory recommended for high speed. You might also find that best looking plugs are obtained with a #3 in the rear and #4 in the front, not unusual according to the Sportster book. It is what I am running these days.

Post Thu Nov 23, 2006 3:23 pm

Posts: 240
Location: Kirkland, WA, USA

You are absolutely correct Patrick, I forgot I have KR heads on and use the longer plugs. I used the Harley number 4 when I ran stock heads. If you put the longer ones in with stock lift it is not likely to hit them, but they could get stuck in there as carbon build up on the exposed threads.

Sorry about any confusion.

Post Thu Nov 23, 2006 7:00 pm

Posts: 323
Location: north central Ma.
I've been using NGK B-6L in my 52 K with good luck over 1000 miles and no plug changes!

L = 7/16 thread reach
H = 1/2
E = 3/4

Book calls for L's

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Post Fri Nov 24, 2006 3:50 am

Posts: 54
I have also seen the B6L recommendation. Never had an original HD plug in hand, so I don't know their thread length. Difference is only 1/16" so it depends on the exact geometry of your insert. The HS plugs are easier to find.

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