Misfire an One Black Plug
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Stage III
Joined: Oct 2022
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From: VT
Misfire an One Black Plug
I know the subject of the rear cylinder having a “Blacker” plug has been beat. But no one has mentioned the difference between an oil burn black, too rich black and too cold black. This spring I bought a 2005 Sportster XL 1200C with a Micuni 42 carb. It ran perfectly that day. The next day I put the same but new air filter on. Then at neutral throttle positions while riding it would pop and sputter. Idle and acceleration were fine. So I put the old air filter back on which was oily and very dirty. Then after a few minutes down the road the engine light came on and became very rough running. I barely got home and then checked for service codes. The codes for battery high, crank position sensor and MAP air sensor came on. I tightened the battery cables and replaced the other two parts. All the codes went away, but the bike remained rough but especially at neutral throttle. I took the bike to a local bike shop, a dad and son business for over 30 years and highly recommended. I asked him to check it out, replace the plugs, put the new air filter back on, new wires and fluids. When I picked it up a week later he said he had to replace the main jet and the float/fuel needle/valve. He said the bowl was overflowing. He said the Micuni was a great carb for the bike but it, while better, still was running rich. He said it was as lean as he could get it without a dynamometer. Well it did run better that day, but the next day and following days it became worse and worse. It’s not rideable now. I should also mention that the exhausts are straight through with no baffles/muffler. Yes I am going to take it back to him, but I want to understand. Thanks.
Stellar HDF Member
Joined: Feb 2013
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From: Dallas, Texas
It's time for you to get your hands dirty. Take the fuel bowl off and *** exactly what jets are in it. Your " mechanic" is NOT TRUSTWORTHY. I just put a MIKUNI HSR 42 on my Wife's 04 1200C. Intermediate jet - 17.5, main jet - 155. Use the Mikuni Set Up instructions and you will be good to go. Ya don't need a Dyno run to lean out your jetting, just some common sense. Ya might wanna check for a vacuum leak at the intake manifold to head area.
Last edited by TexasScooterTrash; Oct 11, 2022 at 07:47 AM.
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Stage III
Joined: Oct 2022
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From: VT
Agreed and Thanks
It's time for you to get your hands dirty. Take the fuel bowl off and *** exactly what jets are in it. Your " mechanic" is NOT TRUSTWORTHY. I just put a MIKUNI HSR 42 on my Wife's 04 1200C. Intermediate jet - 17.5, main jet - 155. Use the Mikuni Set Up instructions and you will be good to go. Ya don't need a Dyno run to lean out your jetting, just some common sense. Ya might wanna check for a vacuum leak at the intake manifold to head area.
Thanks for the push and info. ~ Al
HDF Community Team
Joined: Dec 2011
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From: San Diego, CA
My bike is almost 32 years old and both plugs look the same. I suspect an intake or carburetion issue. Straight pipes don't help and can be difficult to properly tune.
John
Last edited by John Harper; Oct 11, 2022 at 01:42 PM.
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Stage III
Joined: Oct 2022
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From: VT
Yes straight pipes are an issue
I was not aware there was an issue with the rear cylinder having black plugs. I have rarely read a post about this, so I don't think it's been "beat."
My bike is almost 32 years old and both plugs look the same. I suspect an intake or carburetion issue. Straight pipes don't help and can be difficult to properly tune.
John
My bike is almost 32 years old and both plugs look the same. I suspect an intake or carburetion issue. Straight pipes don't help and can be difficult to properly tune.
John
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mike_stahl2000
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Aug 22, 2010 10:55 PM
