Well, I guess no one with a Duke is going to chime in, so...
SPARK PLUG NGK DPR8EA-9
Just run it as is out of the box. I have never had one off.
The gap should be between 0.8mm and 0.9mm.
On my 640 enduro, I have to take the tank off just to see the plug.
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2011 Husaberg TE 300
2002 640 LC4e
Past Rides
'03 KTM 450 EXC (SOLD)
'01 Honda XR650R (SOLD)
'98 Honda XR600R (SOLD)
'95 KTM 620 RXC (SOLD)
'88 Yamaha TT600 (SOLD)
'86 Yamaha XT 350 (SOLD)
'84 Yamaha IT465 (STOLEN)
'83 Kawasaki KDX 450 (SOLD)
'83 Honda CB1000 Custom (SOLD)
'82 Kawasaki KDX 400 (SOLD)
'77 Yamaha DT200 (SOLD)
'70 Honda CT70 (SOLD)