'97 FHLR Backfire w/Black Smoke Rear Cylinder - Harley Davidson Forums: Harley Davidson Motorcycle Forum
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post #1 of 14 (permalink) Old 10-30-2019, 12:26 PM Thread Starter
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'97 FHLR Backfire w/Black Smoke Rear Cylinder

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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post #2 of 14 (permalink) Old 10-30-2019, 01:24 PM
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Check the Coil to see if it's Cracked.
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post #3 of 14 (permalink) Old 10-30-2019, 02:09 PM Thread Starter
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Originally Posted by Ddaddyo View Post
Check the Coil to see if it's Cracked.
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?
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post #4 of 14 (permalink) Old 10-30-2019, 04:10 PM
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Intake seals, sounds like rear has vacuum leak
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post #5 of 14 (permalink) Old 10-30-2019, 04:22 PM
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Originally Posted by tjnoffy View Post
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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post #6 of 14 (permalink) Old 10-30-2019, 08:54 PM
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Quote:
Originally Posted by tjnoffy View Post
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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post #7 of 14 (permalink) Old 10-30-2019, 10:20 PM Thread Starter
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Originally Posted by <G Man> View Post
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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post #8 of 14 (permalink) Old 10-31-2019, 08:17 AM
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Quote:
Originally Posted by tjnoffy View Post
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.

Disclaimer : Don't believe anything I say unless you are absolutely sure that I know what I'm talking about .
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post #9 of 14 (permalink) Old 11-02-2019, 10:36 AM Thread Starter
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Originally Posted by FritzHD View Post
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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post #10 of 14 (permalink) Old 11-02-2019, 12:52 PM
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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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