Hello all,

I'm chasing down an stumbling and backfire condition on my 1998 FXDL low rider.
It runs great after you get rolling but will have a quick stumble/cough sometimes when starting off.
It will always backfire when using the motors compression slowing down.
I thought it might be the lack a baffles in the exhaust from the previous owner.
I put on some new 3" Cobra Slip On's yesterday and it is still stumbling and backfiring.
I also tried a set of new NGK plugs but that did not seem to help either. So now I'm thinking
something is going on with the carburetor? Here is a picture of the old Autolite plugs... to me they look like the carb is jetted properly.
Any thoughts or other things to check would be greatly appreciated.

 

Check for leaks around the intake and exhaust.

 

hard to tell from a pic looks lean to me backfire when you let off means it is lean or timing issues

 

Sure you're not just getting decel pop? It can be loud depending on how hard you decelerate and your A/F mixture. When mine is cold it may cough a little bit or if I've been running down the interstate and I blip the throttle to rev match it may or may not cough, but it's not often... not often enough to worry about it.

 

forgot the other problem the stumble could be the accelerator pump

 

since you've changed pipes & most likely not sure on how the carb is jetted I would start there , with todays gas it's a bit hard to tell from the plugs , your center are a tad brown & the thread area is black , 98 has a CV carb unless the po changed it , if still CV it's a easy check on the jets , & also check for air leaks around the intake & pipes at heads & mufflers

 

My 98 FLHT did that when a vac hose came off the VOES

 

As mentioned above, Stumbling = accelerator pump mixture. When you snap the throttle does it stumble, is a good test.

 

Thanks for all the replies... I will double check for any air intake leaks as well as the vacuum lines today. I'm going to pull off the carb and remove the plug for the air/fuel mixture screw so I can see if it can be adjusted out that way.

 

What about the relays, how old are they ?