107 M8 Spark Plug Gap
Thread Starter
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Road Captain
Joined: Nov 2018
Posts: 614
Likes: 231
From: Hendeson, NV
107 M8 Spark Plug Gap
My 2019 Low Rider has the 107 M8 engine with a Stage 1 upgrade. I have approximately 8k miles on the new set of SE spark plugs I had the dealer install. Over the last 5 months, I noticed the engine is getting progressively more difficult to turnover when starting. So, I removed a spark plug for inspection and noted 1> the firing tip, ground electrode and the tip of the insulator needed cleaning to remove a black gritty substance, and 2> the gap on the spark plug was just barely under .04". I checked the owner's manual, and it showed the gap should be between .03" & .04". The SE spark plugs come from the factory with a gap of .031".
Questions.
1. Why did the dealer maintenance department increase the gap to .04"?
2. Where are you setting the gap on your M8 engine spark plugs?
3. Considering installing NGK iridium spark plugs; anyone running the iridium spark plugs and your results?
Questions.
1. Why did the dealer maintenance department increase the gap to .04"?
2. Where are you setting the gap on your M8 engine spark plugs?
3. Considering installing NGK iridium spark plugs; anyone running the iridium spark plugs and your results?
Seasoned HDF Member
Joined: Aug 2017
Posts: 7,323
Likes: 11,760
From: Omaha,NE
My 2019 Low Rider has the 107 M8 engine with a Stage 1 upgrade. I have approximately 8k miles on the new set of SE spark plugs I had the dealer install. Over the last 5 months, I noticed the engine is getting progressively more difficult to turnover when starting. So, I removed a spark plug for inspection and noted 1> the firing tip, ground electrode and the tip of the insulator needed cleaning to remove a black gritty substance, and 2> the gap on the spark plug was just barely under .04". I checked the owner's manual, and it showed the gap should be between .03" & .04". The SE spark plugs come from the factory with a gap of .031".
Questions.
1. Why did the dealer maintenance department increase the gap to .04"?
2. Where are you setting the gap on your M8 engine spark plugs?
3. Considering installing NGK iridium spark plugs; anyone running the iridium spark plugs and your results?
Questions.
1. Why did the dealer maintenance department increase the gap to .04"?
2. Where are you setting the gap on your M8 engine spark plugs?
3. Considering installing NGK iridium spark plugs; anyone running the iridium spark plugs and your results?
Thread Starter
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Road Captain
Joined: Nov 2018
Posts: 614
Likes: 231
From: Hendeson, NV
You may be correct. I run the HD LiFE lithium ion battery. Have not been satisfied with starting capability since 6 months after purchase.
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Road Captain
Joined: Jul 2011
Posts: 516
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From: dunedin, fl
aint plug gap
I would pay attention to plugs being black. they should be light brown, almost tan. Maybe reload the stock tune instead of Stage 1 and try and see if it starts better. The blackness indicates oil or way too rich a mixture from ECM.