Occasional startup issue after swapping spark plug wires
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Cruiser
Joined: Mar 2020
Posts: 137
Likes: 132
From: Los Angeles
Occasional startup issue after swapping spark plug wires
Looking for advice. A couple of weeks ago, I swapped out the stock spark plug wires on my 2020 Softail Slim with the red HD "phat 10mm spark plug wires" and now I'm having the occasional startup issue where the bike is sometimes struggling to start up. I had the bike serviced for its 10k service back in March of this year which included replacing the spark plugs with NGK Iridium CR9EIX ones. I'm seeing a couple of youtube vids and a couple of articles saying that the wires and plugs should be replaced at the same time due to potential "cross contamination" between the new wires and the old plugs. Should I have replaced the spark plugs when I swapped out the wires anyway? Thanks in advance!
Stage I
Joined: Oct 2023
Posts: 1
Likes: 1
From: Hudson WI
RES 10MM Spark Plug Wire Swap
I am having the same issue with my 2010 FXSTCI since swapping out the spark plug wires with the RED 10MM Harley ones. I put the old plug wires back on and get the same thing. When it turns over it sounds like the timing is off, woofs a little. Things I checked so far:
1. All fuses including fuel pump fuse were good.
2. When I turn the ignition on I hear the fuel pump kick in and there's bubbles in the fuel tank.
3. I thought I may have old fuel so I siphoned it out and relaced with 4 gal. fresh Unleaded Premium.
4. Charged the battery and had it tested. 12.6-7 Volts, 326 CCA (above specs - 310), Cleaned battery terminals and all contacts.
5. There is spark and fuel in both cylinders, checked plug gap.
6. Checked for diagnostic codes; none.
I don't know what to check next. All help is appreciated. I live in west central Wisconsin, it's 87 degrees out, and my bike won't start....
Sometimes when you do something ridiculous, you learn a lot in the process!
PLUG WIRES WERE REVERSED....
1. All fuses including fuel pump fuse were good.
2. When I turn the ignition on I hear the fuel pump kick in and there's bubbles in the fuel tank.
3. I thought I may have old fuel so I siphoned it out and relaced with 4 gal. fresh Unleaded Premium.
4. Charged the battery and had it tested. 12.6-7 Volts, 326 CCA (above specs - 310), Cleaned battery terminals and all contacts.
5. There is spark and fuel in both cylinders, checked plug gap.
6. Checked for diagnostic codes; none.
I don't know what to check next. All help is appreciated. I live in west central Wisconsin, it's 87 degrees out, and my bike won't start....
Sometimes when you do something ridiculous, you learn a lot in the process!
PLUG WIRES WERE REVERSED....
Last edited by TomHFXSTCI; Oct 2, 2023 at 03:40 PM. Reason: FIxed problem
Thread Starter
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Cruiser
Joined: Mar 2020
Posts: 137
Likes: 132
From: Los Angeles
I am having the same issue with my 2010 FXSTCI since swapping out the spark plug wires with the RED 10MM Harley ones. I put the old plug wires back on and get the same thing. When it turns over it sounds like the timing is off, woofs a little. Things I checked so far:
1. All fuses including fuel pump fuse were good.
2. When I turn the ignition on I hear the fuel pump kick in and there's bubbles in the fuel tank.
3. I thought I may have old fuel so I siphoned it out and relaced with 4 gal. fresh Unleaded Premium.
4. Charged the battery and had it tested. 12.6-7 Volts, 326 CCA (above specs - 310), Cleaned battery terminals and all contacts.
5. There is spark and fuel in both cylinders, checked plug gap.
6. Checked for diagnostic codes; none.
I don't know what to check next. All help is appreciated. I live in west central Wisconsin, it's 87 degrees out, and my bike won't start....
Sometimes when you do something ridiculous, you learn a lot in the process!
PLUG WIRES WERE REVERSED....
1. All fuses including fuel pump fuse were good.
2. When I turn the ignition on I hear the fuel pump kick in and there's bubbles in the fuel tank.
3. I thought I may have old fuel so I siphoned it out and relaced with 4 gal. fresh Unleaded Premium.
4. Charged the battery and had it tested. 12.6-7 Volts, 326 CCA (above specs - 310), Cleaned battery terminals and all contacts.
5. There is spark and fuel in both cylinders, checked plug gap.
6. Checked for diagnostic codes; none.
I don't know what to check next. All help is appreciated. I live in west central Wisconsin, it's 87 degrees out, and my bike won't start....
Sometimes when you do something ridiculous, you learn a lot in the process!
PLUG WIRES WERE REVERSED....
Seasoned HDF Member
Joined: Mar 2010
Posts: 38,623
Likes: 6,442
From: Honah Lee
Looking for advice. A couple of weeks ago, I swapped out the stock spark plug wires on my 2020 Softail Slim with the red HD "phat 10mm spark plug wires" and now I'm having the occasional startup issue where the bike is sometimes struggling to start up. I had the bike serviced for its 10k service back in March of this year which included replacing the spark plugs with NGK Iridium CR9EIX ones. I'm seeing a couple of youtube vids and a couple of articles saying that the wires and plugs should be replaced at the same time due to potential "cross contamination" between the new wires and the old plugs. Should I have replaced the spark plugs when I swapped out the wires anyway? Thanks in advance!
May be the plugs. Especially if you do mostly around town and then a hot long interstate run.
That type of plug is easy to cold foul on a Harley. Now they will go 100k in a Honda car.
The original conventional plugs are much better.
Now that's just my opinion of what I've experienced. They need high voltage spark and perfect fuel air ratio. That small tip if it gets a tad of carbon on it will glaze over with a hot run.
Then it's like it has a glass insulation over it.
Unless your Harley sits in the sun and such, the wires should last a long time. My 04 has the original on it. That silliness that they match the plugs. Tin men spin that BS.
Last edited by Jackie Paper; Oct 2, 2023 at 05:06 PM.
Road Master
Joined: Jun 2013
Posts: 1,058
Likes: 953
From: Sarasota Florida
When I put the 10mm wires on my Fatboy, I got a check engine light that was constant. I took the bike to the dealer and they told me the light was on because "I tried to start the bike without any spark plug wires." And they called themselves mechanics.
Months later, I was talking to a dyno guy and happened to mention the check engine light. He said that it was because of the 10mm spark plug wires. So I put the stock ones back on and no more check engine light.
I would put your stock wires back on and go from there
Months later, I was talking to a dyno guy and happened to mention the check engine light. He said that it was because of the 10mm spark plug wires. So I put the stock ones back on and no more check engine light.
I would put your stock wires back on and go from there
Seasoned HDF Member
Joined: May 2018
Posts: 5,814
Likes: 7,147
From: Las Vegas
May be the plugs. Especially if you do mostly around town and then a hot long interstate run.
That type of plug is easy to cold foul on a Harley. Now they will go 100k in a Honda car.
The original conventional plugs are much better.
Now that's just my opinion of what I've experienced. They need high voltage spark and perfect fuel air ratio. That small tip if it gets a tad of carbon on it will glaze over with a hot run.
Then it's like it has a glass insulation over it.
Unless your Harley sits in the sun and such, the wires should last a long time. My 04 has the original on it. That silliness that they match the plugs. Tin men spin that BS.
That type of plug is easy to cold foul on a Harley. Now they will go 100k in a Honda car.
The original conventional plugs are much better.
Now that's just my opinion of what I've experienced. They need high voltage spark and perfect fuel air ratio. That small tip if it gets a tad of carbon on it will glaze over with a hot run.
Then it's like it has a glass insulation over it.
Unless your Harley sits in the sun and such, the wires should last a long time. My 04 has the original on it. That silliness that they match the plugs. Tin men spin that BS.
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HDF Community Team
Joined: Oct 2018
Posts: 4,347
Likes: 3,392
From: Seattle
"NGK Iridium CR9EIX ones"
I would highly recommend NOT buying these unless you can verify where they came from and the shop knows they're legit ones they're selling.
These plugs got targeted by counterfeiters and the market was flooded with fake ones.
This is why I decided to get the SE Sparkplugs instead. They arent targets for counterfeiters.
Plus it doesnt seem that these Iridium/performance spark plugs are of much advantage in an M8 either.
The stock ones are pretty good.
I would highly recommend NOT buying these unless you can verify where they came from and the shop knows they're legit ones they're selling.
These plugs got targeted by counterfeiters and the market was flooded with fake ones.
This is why I decided to get the SE Sparkplugs instead. They arent targets for counterfeiters.
Plus it doesnt seem that these Iridium/performance spark plugs are of much advantage in an M8 either.
The stock ones are pretty good.
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Seasoned HDF Member
Joined: May 2018
Posts: 5,814
Likes: 7,147
From: Las Vegas
"NGK Iridium CR9EIX ones"
I would highly recommend NOT buying these unless you can verify where they came from and the shop knows they're legit ones they're selling.
These plugs got targeted by counterfeiters and the market was flooded with fake ones.
This is why I decided to get the SE Sparkplugs instead. They arent targets for counterfeiters.
Plus it doesnt seem that these Iridium/performance spark plugs are of much advantage in an M8 either.
The stock ones are pretty good.
I would highly recommend NOT buying these unless you can verify where they came from and the shop knows they're legit ones they're selling.
These plugs got targeted by counterfeiters and the market was flooded with fake ones.
This is why I decided to get the SE Sparkplugs instead. They arent targets for counterfeiters.
Plus it doesnt seem that these Iridium/performance spark plugs are of much advantage in an M8 either.
The stock ones are pretty good.
Last edited by 702; Oct 2, 2023 at 08:00 PM.
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