1200 Iron misfire.
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6th Gear
Joined: Oct 2025
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From: Nicosia Cyprus
1200 Iron misfire.
I think I have posted in the wrong section of the forum, so here I repeat myself.
Dear all,
Thank you for accepting me into this excellent forum.
I'm a newbie as far as Harleys are concerned, but I took the plunge and got myself a 2019 1200 Iron with stage 1 tuning, with 32000 KM on the clock, a couple of months ago. I love the bike and want it to be perfect.
I noticed that in 1st and 2nd gear, the engine would misfire under 2000rpm, which would clear out above 2000 rpm. I changed spark plugs to Iridium, but the misfire was still there. I measured the resistance of the coil and ignition wires, and the wires had higher resistance than the acceptable range. I changed to new ones, and the mifire goes mostly away when the engine is at normal operating temperature. I have to say that I vent the PCV fumes now into the air. My take is that due to the years the engine was breathing in the oil fumes into the throttle body, and due to the carbon buildup on the pistons, it pre-ignites low down. In the older days, we used to squirt a little water down the throttle body, and the steam would loosen the carbon up and spit it out the exhaust.
Can I use this method to decarbonize? BTW, I looked through a camera lens inside, and the crown of the pistons indeed have carbon on them.
Dear all,
Thank you for accepting me into this excellent forum.
I'm a newbie as far as Harleys are concerned, but I took the plunge and got myself a 2019 1200 Iron with stage 1 tuning, with 32000 KM on the clock, a couple of months ago. I love the bike and want it to be perfect.
I noticed that in 1st and 2nd gear, the engine would misfire under 2000rpm, which would clear out above 2000 rpm. I changed spark plugs to Iridium, but the misfire was still there. I measured the resistance of the coil and ignition wires, and the wires had higher resistance than the acceptable range. I changed to new ones, and the mifire goes mostly away when the engine is at normal operating temperature. I have to say that I vent the PCV fumes now into the air. My take is that due to the years the engine was breathing in the oil fumes into the throttle body, and due to the carbon buildup on the pistons, it pre-ignites low down. In the older days, we used to squirt a little water down the throttle body, and the steam would loosen the carbon up and spit it out the exhaust.
Can I use this method to decarbonize? BTW, I looked through a camera lens inside, and the crown of the pistons indeed have carbon on them.
Grand HDF Member
Joined: May 2014
Posts: 3,843
Likes: 1,174
From: florida
your bike should never see less than 2000 rpm except when slipping the clutch to get out of 1rst gear,,,,,,ever.
sportsters are ment for the engine to spin, if you are trying to cuise ant any rpm under 2k youa re lugging the bike, not a good thing.
m
sportsters are ment for the engine to spin, if you are trying to cuise ant any rpm under 2k youa re lugging the bike, not a good thing.
m
Seasoned HDF Member
Joined: Aug 2008
Posts: 5,071
Likes: 1,006
lugging is true, IF, you are over loading it but 1 & 2 at 2k should not do that.
as far as water, it takes more than a spritz, it must be over time. if you think carbon build up, best to go with a chemical agent made for that.
i ran water injection on my 440 and true carbon wasn't a thing, mostly to control pre-ignition and detonation. of note, there must be a controlled application aka, temperature and absolute manifold pressure.
but mr. marcodarq is right, the hd does not like running at 2k.
all engine will produce a coating on the pistons, so post pictures, the type of build up matters, from a black haze to a crusty mess.
as far as water, it takes more than a spritz, it must be over time. if you think carbon build up, best to go with a chemical agent made for that.
i ran water injection on my 440 and true carbon wasn't a thing, mostly to control pre-ignition and detonation. of note, there must be a controlled application aka, temperature and absolute manifold pressure.
but mr. marcodarq is right, the hd does not like running at 2k.
all engine will produce a coating on the pistons, so post pictures, the type of build up matters, from a black haze to a crusty mess.
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