Ok time to show my complete Harley noob-ness lol...

From the time I bought this bike ('09 FXD) a month ago it has had this.. Im guessing what you guys are calling a decel pop. Basically what others here in the south refer to as "racking the pipes" ...

Not a backfire ... just a sort of rumbling "pop pop pop pop pop..." under decel or downshift situations..

Was told by the dealer that the pipes were aftermarket and they dont seem to have baffles so I assumed this was normal? ... In my reading here and other places Im starting to get the idea that is not the case and its showing a lean condition... Note that the A/C is stock. Havnt checked the plug color yet but I will after my trip home on the morning.

Please advise... If this is and issue that needs to be addressed I'll have my dealer do it ASAP.

 

Decel popping is NOT necessarily from a lean condition.

It is unburnt fuel that is burning in the exhaust.
There is always going to be some unburnt fuel in the exhaust...even if you are running lean.

Decel pop occurs when:

1. You are running so lean that the exhaust is superheated, then you will get decel pop from that.

2. You are NOT to lean, but have the correct air/fuel mixture in the exhaust for it to burn. This most often occurs when there are higher than stock flowing pipes which increase the air in the exhaust and results in decel pop.

In MOST cases decel pop is NOT from being too lean. But it can be cured by richening up the air/fuel so that the ratio is no longer conducive to burning and instead get expelled out the end of the pipe unburnt.

If you are not running too lean (and decel popping is NOT the way to know) and want to get rid of it, you will need to richen up your mixture more than it needs to be to run optimally so that it will stop.

Another choice is to change the air in your pipes with baffles or Thunder Torque inserts. By reducing the air you are richening up the A/F mixture in the pipes and may stop the popping that way.

 

Thanks for that explanation Kevin.. I think that answers the question nicely. I'll have a look at the plugs just to be safe. The poping is a bother at all I just got the impression from a few reads that it might be a indicator of a worse condition.

 

That's a very good explanation

 

My stock FXDC pipes pop. I like it!

My old Ironhead Sportster and British Vertical Twins did it too, and that is with the carbs dialed in so the plug color looked correct.

Wonder how many of the younger guys read plugs? I would just rather ride than adjusting chains, valves and carbs. Getting old I guess.

 

I have a 2010 FXD and it sounds like the same problem. I still have the OEM A/C and its has rush slip ons. So Kevin if im reading you right the mixture needs to be programed to be richer?

 

My bike does the same thing and its tuned perfect.

 

No matter what, you'll get a little bit of decel pop, particularly from the rear cylinder. Most of the popping occurs because under closed throttle, high rpm, the engine is under high vacuum. Even with the best tunes, some throttle positions don't allow for richening to a safe level. The slightly lean condition, plus the hotter rear cylinder, causes the fuel during the overlap period to ignite on the heated exhaust valve resulting in a pre-ignition. That's the burbling pop on decel you might hear. When the engine is hotter, there is a chance for some popping from the front as well.

If the pops are louder than burbling pops, you could have a leaky exhaust gasket or a bad tune.

 

My 2011 Limited never did it but my 08 Roadking does & it drives me crazy. Exact same stage 1 setup but the King I haven't had dyno tuned yet. Hoping the tune solves it for me.

 

Very good info. I've been in the same position with my 2010 FXDC. If the OP is sure he doesn't have any exhaust leaks, he could roll the dice and see if a pair of XIED's might correct the popping. I had XIED's on mine and it still popped. Instead of going with a full blown tuner, I elected to go with a Dobeck TFI since all I needed to do was add a tick more fuel. Problem solved.