Question about 2006 Harley Davidson FLSTF Fat Boy

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Backfire exhaust Bike sat for a while, when started it backfires through exhaust, sometimes flames in exhaust. Have carb cleaner in tank but no help. Plugs are tan in color. Any ideas?

Posted by Anonymous on


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Hi Anonymous, flames are a prime indicator of retarded timing which means you probably have an electrical component going south. But which one is the million dollar question. Not quite sure about the carb cleaner in the fuel tank, like what effect does carb cleaner have on sensors? my gut says not good but I could be wrong. That being said you need to do some on board diagnostics. go to and they will walk you through it. Good luck

Posted on Apr 18, 2015


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Posted on Jan 02, 2017

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SOURCE: 1981 Wide Glide Bike is missing and backfiring

open up the ignition cover plate and check the backing plate. it may have come loose and threw the bike out of time.
make sure your plug wires are plugged on tight and the coil wires are secure.
It is most definitely a timing problem.

Posted on Jun 06, 2009

  • 202 Answers

SOURCE: Bike is backfiring through carb.

do u have the correct spark plug the one recommended by the manufacturer

Posted on Aug 02, 2009

  • 330 Answers

SOURCE: 2004 HD sportster. bike sit while deployed for 7

Make sure firing order is correct for the plugs.Also compression test is easy way to make sure valves are working.was it doing this before rebuild carbs.Thank you for your service, I am greatfull for the FREEDOM!!!!

Posted on Apr 20, 2010

  • 4 Answers

SOURCE: backfire

Check no split in exhausted

Posted on Jun 24, 2013

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1 Answer

How do I stop my bike from constant backfiring?

its running lean. Could be a vent problem with the gas tank. try running with the gas lid slightly open.. if this doesn't work increase the jet size in the carbs.

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Backfires at idle (sometimes) but seems through air intake not exhaust ? Bike struggles to start without choke when warm ??

A bike that backfires through the carb has ignition timing that is too far advanced. This will also cause bad starting. Get the timing fixed.

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dean ,carb cleaner can be used to clean the carb parts on a re build and thats all .if the bike sat over winter (with fuel in the tank ?) how does it smell ? if its bad it will smell like turpentine .and needs to be changed ,theirs a lot of questions here . was the batt in good shape from the winter ,(good charge 12.6 ?) was your choke on when you dumped the cleaner in tryin to start ?

Apr 15, 2014 | 2006 Harley Davidson FLSTF Fat Boy

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If the bike was running correctly when it was put in storage two years ago, I would start with the easy things first: As the previous poster suggested, install new, correctly gapped plugs, along with a new battery. Your bike uses an electronic ignition system, and it will not opporate correctly if you have a bad battery. The bike will miss, pop, and backfire, because there is not enough electrical power in storage (battery) to properly run the ignition system.

If these two things do not get the bike running correctly you will need to look at the carbs. Was the bike stored with fuel in the tank and carbs? If so, this is the most likely reason for the bike not wanting to run correctly. Flames from the exhaust are an indication of a very rich fuel/air mixture (a float could be stuck open (it can also be caused by the ignition not working properly and allowing unburnt fuel into the exhaust system)). Cleaning and reassembling mulitple carborators is not that difficult if you are careful and reasonably handy, but tuning them properly can be very difficult. You can save a lot of money if you rebuild them yourself, then take the bike to the shop to be tuned (The standard service rate these days is around $75 an hour)

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Prob miles off here but my zx7r did this after being sat 20 months. Turned out it simply had exhaust gaskets totally inoperable. The block where the pipes come out, therefore was in fact sucking air in as the hot fumes were spitting out, mixing up and creating a mini explosion. Check pipes are all sealed nicely tightly. Everything else you did sounds right. What about lifting tank off - airbox off (check that) and look at carbs? clean? Sounds daft this but is it sat with 2 year old petrol in the tank too? It's as if the mixture is going in, plug is igniting but then like its no compression? Mine 'was' simply exhaust gaskets. Think they would do the same if you totally stripped the whole exhaust off and tried starting with a couple of dirty great holes in your bore. Will it not even start with jump leads to a large car battery? Did mine to our landrover and forced it to start - endless charge from running landrover. Take a plug out, connected to your HT lead, turn it over but touching / earthing plug onto part of your metal frame / casing. Should see the actual spark, if not its your coil / ht leads??? Not an expert just had Kwakker long time lol. Love hate relationship.

Jun 08, 2013 | 1993 kawasaki ZXR 750

1 Answer

Bike sat up for 3 or 4 years. recently cleaned the carb, changed the plug and oil and bike started. Tried starting it recently and it wont. Seem to be backfiring sometimes when kicking it over.

clean plug .. although new plug if old fuel or unbalanced carb it may quickly foul. if this works you may need help to work out whats causing plug to foul.

Mar 10, 2013 | 2001 Yamaha YZ 426 F

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My 2007 suzuki boulevard 1500 has poor throttle responce when you dont expect it.When starting off from an interection it will sometime pop through the trrottle bodies instead of exelerating and possible...

get some carb cleaner and start the motor then spray the carb cleaner around the outside ot the intake to check for leaks. I have seen several just like that and the intake manifolds was leaking air through them. If yours is leaking when you spray the carb cleaner on them the motor will rev letting you know it is sucking the cleaner into the motor.

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1 Answer

When at idle it shuts off and while down shifting it backfires

You may be experiencing ethanol fuel , it can lower your idle. Use the idle adjust screw on the carburetors to raise the isle enough it wont kill. If the carbs are dirty use a fuel system cleaner in the tank like Chevron Techron to clean the varnish/gum out of the carbs. Backfiring is caused by air leaks in the exhaust system , usually the copper o-rings in the exhaust port where the pipe plugs into the head. Sometimes a bad gasket between the head pipe and the muffler is the cause of the backfire. When exhaust systems are replaced the gaskets are often reused , when they fail you get air leaks that cause popping and backfiring.

Aug 27, 2010 | 2000 Honda VT 1100 C Shadow Spirit

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2004 HD sportster. bike sit while deployed for 7 months. Tried to start it and it cranks over and backfires through the exhaust and carb and will not start. Rebuilt carb and changed intake seals. Still...

Make sure firing order is correct for the plugs.Also compression test is easy way to make sure valves are working.was it doing this before rebuild carbs.Thank you for your service, I am greatfull for the FREEDOM!!!!

Apr 20, 2010 | 2004 Harley Davidson XL 1200 C Sportster...

1 Answer

Generator hard to start and backfiring

Sound like you've done things in the correct order, tecumseh's are notorious for carb problems if you let as sit in them. Backfiring is timing related (flywheel key) or valve problems. I would take a closer look at the exhaust valve I don't believe it is closing all the way.

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