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Discussion Starter #1
This morning when starting my '97 Road King (stock 1340cc and carb w/95k miles [25k on remanufactured motor], header pipes, Pingle petcock), the engine was running as expected on the front cylinder, but missing/sputtering on the rear cylinder with black smoke from the rear cylinder exhaust. Will check spark plugs and plug wire when I get home, but any suggestions on what else to check? Just rode it a week ago (in light rain), and it ran fine. Thanks!
 

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Just Ride
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Intake seals, sounds like rear has vacuum leak
 

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Got it. Thanks. Will check the resistance measurements, too. Just for my edification, what causes the black smoke, and how might a cracked coil cause that?

Black smoke is usually from an excessively rich condition. If the coil was cracked, coil wire bad, spark plug bad or anything else that would cause improper burning of the fuel in the cylinder it will have black smoke coming from the exhaust pipe.
 

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Barney Fife - Poser
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This morning when starting my '97 Road King (stock 1340cc and carb w/95k miles [25k on remanufactured motor], header pipes, Pingle petcock), the engine was running as expected on the front cylinder, but missing/sputtering on the rear cylinder with black smoke from the rear cylinder exhaust. Will check spark plugs and plug wire when I get home, but any suggestions on what else to check? Just rode it a week ago (in light rain), and it ran fine. Thanks!
So, did it do this for a minute and then you shut it off and jumped in a car? Did you ride it to wherever you need to get home from? How long did it smoke? Never did it before? All bikes have header pipes. Are you saying you have true duals so you are sure it was just the rear smoking?
 

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Discussion Starter #7
So, did it do this for a minute and then you shut it off and jumped in a car? Did you ride it to wherever you need to get home from? How long did it smoke? Never did it before? All bikes have header pipes. Are you saying you have true duals so you are sure it was just the rear smoking?
Spent 15 minutes attempting to start it at least 6 times, black smoke from rear cylinder exhaust and sputtering, pulling plug wires, resetting. Never did it before. Had to leave for my 45-mile drive to my DoD job. There was no riding on one cylinder. Yes, true duals... separate pipes for each cylinder and black smoke from only the left pipe (rear cylinder).

Tested the ignition coil. Primary and secondary resistance test good per shop manual. Plugs are black and sooty. Picking up new plugs, cables, ignition coil (while the tank is moved), intake manifold seals tomorrow.

Other suggestions appreciated.
 

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Retired citizen
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Spent 15 minutes attempting to start it at least 6 times, black smoke from rear cylinder exhaust and sputtering, pulling plug wires, resetting. Never did it before. Had to leave for my 45-mile drive to my DoD job. There was no riding on one cylinder. Yes, true duals... separate pipes for each cylinder and black smoke from only the left pipe (rear cylinder).

Tested the ignition coil. Primary and secondary resistance test good per shop manual. Plugs are black and sooty. Picking up new plugs, cables, ignition coil (while the tank is moved), intake manifold seals tomorrow.

Other suggestions appreciated.
Compression test both cylinders.
 

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Discussion Starter #9
Intake seals, sounds like rear has vacuum leak
Before I pull the carb and intake manifold, wouldn't a leaky seal cause the air/fuel mixture to be lean, allowing extra air into the cylinder? Sounds like the black smoke and black, sooty plugs indicate a too rich condition. Or am I making wrong assumptions? Thanks.
 

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Retired citizen
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Intake seal leak test is easy, no disassembly required ! Idle engine and squirt WD-40 or brake cleaner around the intake manifold to head connection, if idle changes the seals are leaking.
 

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Discussion Starter #11
Ok, replaced coil (since I had the tank moved anyway), plug cables, and plugs. Started up and idled great. Test ride next.

Surprised to find both plugs blackened (see attached), not just the one throwing black smoke. Looks like she was/is running rich. May need a carb rebuild.

Thoughts?
 

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Retired citizen
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Those Plugs look rich to me. For a carbed engine they should look dark white to a light tan IMO.
 

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Flats where its at
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clean or replace air cleaner element set low speed jet first if u got one then set idle then last, hi speed lean carb main jet 1/8 turn at a time ["in" is leaner] till its ash brown nice dry tan color is what u want. If its a single throat carb and one cyl is darker than the other u can try the next hotter plug in the richer [usually rear] cly to even them out
To check plugs... [bring your wrench and gloves] run at comfy highway speed a few min... then close throttle and shut off motor, coast bike to a stop THEN re-check plugs; doin it this way = how it runs at highway speed.. again, u want nice tan plug ; remember if one idle's too long before checking, plugs can look rich real quick... but u want is to see how its doin runnin down the road jm2cents
 
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