Spark plugs recommendation
Club Member
Joined: Apr 2016
Posts: 11,620
Likes: 8,447
From: Inland NW
I have used the NGK Iridium, the Denso Iridium, and the Screamin' Eagle Iridium. All work well.
I am sure it is just coincidence, or fuel quility, but I like the Densos. My mileage is consistently awesome, and my 128 runs so good,
I am sure it is just coincidence, or fuel quility, but I like the Densos. My mileage is consistently awesome, and my 128 runs so good,
Seasoned HDF Member
Joined: Mar 2010
Posts: 38,658
Likes: 6,457
From: Honah Lee
Spark plugs are not going to measurable help fuel milage.
Now if your's are worn out it might.
But any of the recommended will perform almost identically.
Now if your's are worn out it might.
But any of the recommended will perform almost identically.
Last edited by Jackie Paper; Yesterday at 09:36 PM.
Seasoned HDF Member
Joined: Jan 2008
Posts: 13,700
Likes: 11,497
From: State of Confusion
curious what sparked your interest (pun intended) in making a change? A properly tuned M8 with clean air filter and proper tire pressure maintained and ridden to not allow carbon build up should get great MPG and service life with OEM spark plugs. Been a successful formula for me. Hell my 25 RG with SE Stage 2 running it real hard most of the time has been averaging 47-48 mpg.
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Stellar HDF Member
Joined: Oct 2007
Posts: 2,969
Likes: 242
From: Kentucky
Was just reading and found something that said with a stage 2 or higher which requires more air and fuel that improved combustion and it mentioned spark plugs may help with mpg.
Seasoned HDF Member
Joined: Mar 2010
Posts: 38,658
Likes: 6,457
From: Honah Lee
Study up on stoichiometry 14.7-1. Beware of people saying what you said in post 6 with the underlying fact that they are selling parts.
Remember gasoline is a terrible lubrication. Back when we had carburetors, cylinders had 0.005 wear or more in 100K. FI motors have little cylinder wear at 200k.
A tuner just changes a FI to a carburetor era.
If you want good fuel mileage and a long engine life, don't drive it like you stole it.
Remember gasoline is a terrible lubrication. Back when we had carburetors, cylinders had 0.005 wear or more in 100K. FI motors have little cylinder wear at 200k.
A tuner just changes a FI to a carburetor era.
If you want good fuel mileage and a long engine life, don't drive it like you stole it.
Last edited by Jackie Paper; Today at 07:58 AM.
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Tourer
Joined: May 2017
Posts: 400
Likes: 339
From: Coastal Carolina
Its time for my first M8 plug change and I wonder what plug as well.
When I purchased my EVO new and then started modding, Cam , S&S Carb etc she became VERY plug picky ( heat range I assume, something you hear little talk about now days)
30 years ago the 2 ( NOT 4 ) plugs were so easy to get at ( NO removing gas tank required ) and me being young and eager to turn a wrench and I had plenty of $ back then I decided to set out on a quest and try ALL the spark plugs and find the best running plug!
I started with ALL the Harley plugs, then Harley SE, moved to Champion ( the one who made the Harley plug ) to Bosch, Accel, U grove, E3, platinum, double platinum, Iridium, etc If a plug was made to fit my 1997 Harley I tried it over the last 29 years of owning her.
I settled on the best running plug, The least expensive of the bunch! a $3 copper Autolite!
My goal was not what plug lasted longer but what plug ran the best in the engine.
Some say no way a plug feels different but my butt dyno , easy or hard starts, even the sound ( I'm a sound engineer, so I hear things others don't ) but my bike and I stuck with the autolite ( with that First brands / Fram crap I'm stocking up on NOS eBay Autolites )
The M8 is NOT a quick EZ plug change like my EVO so I hope to learn what plug runs best in a Stage 2 107 M8 BEFOR I change mine out for the first time.
Back in my EVO days, I had no Harley Forums or even internet to help me research, I had to actually buy and try each plug to find the best plug in my bike.
I hope the best plug question is not the same as the best oil question? LOL
When I purchased my EVO new and then started modding, Cam , S&S Carb etc she became VERY plug picky ( heat range I assume, something you hear little talk about now days)
30 years ago the 2 ( NOT 4 ) plugs were so easy to get at ( NO removing gas tank required ) and me being young and eager to turn a wrench and I had plenty of $ back then I decided to set out on a quest and try ALL the spark plugs and find the best running plug!
I started with ALL the Harley plugs, then Harley SE, moved to Champion ( the one who made the Harley plug ) to Bosch, Accel, U grove, E3, platinum, double platinum, Iridium, etc If a plug was made to fit my 1997 Harley I tried it over the last 29 years of owning her.
I settled on the best running plug, The least expensive of the bunch! a $3 copper Autolite!
My goal was not what plug lasted longer but what plug ran the best in the engine.
Some say no way a plug feels different but my butt dyno , easy or hard starts, even the sound ( I'm a sound engineer, so I hear things others don't ) but my bike and I stuck with the autolite ( with that First brands / Fram crap I'm stocking up on NOS eBay Autolites )
The M8 is NOT a quick EZ plug change like my EVO so I hope to learn what plug runs best in a Stage 2 107 M8 BEFOR I change mine out for the first time.
Back in my EVO days, I had no Harley Forums or even internet to help me research, I had to actually buy and try each plug to find the best plug in my bike.
I hope the best plug question is not the same as the best oil question? LOL
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Seasoned HDF Member
Joined: Jan 2008
Posts: 13,700
Likes: 11,497
From: State of Confusion
never mind, those OEMs work great also
Last edited by mjwebb; Today at 09:12 AM.
