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Back firing through air cleaner

Have you load tested battery to check CCA ???????? Might be a place to start.
 
Don't overlook the neg cable connetion to frame.
Another thing I have noticed is when it happened to me, is that it almost always happened when I jacked the throttle befor shut down, than when I went to re start the bike I would get extended crank and when releasing the starter button befor the engine had started a backfire into the intake would happen.
 
Check the electric automatic compression release connections. Should be a connection right near the base of the fuel tank. When they dont work that battery and starter can take a real beating. You may need a wiring diagram for your year or just find the wires from the CR's and follow them back...
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Thanx Jack & Bodeen ! This Hard-start issue, not only has me stumped at the moment....over a considerable amount of time has been a very slow maturing issue. This is on my 2012 103 ci FLHX. It didn't just start happening one day. When it 1st started to happen, it was VERY rare & would only happen when the engine was Hot, and after sitting "Off" as I stopped for a gas or stretch your leg(s) break ! It happened so RARELY that I blamed bad-gas, at 1st. So when this hard-start issue 1st started, which was once in a great while, the engine would turn over perfectly fine but wouldn't "fire" ! But instead would either "pop", w/a puff of smoke out the intake (air-filter) or it would back-fire (A very low deep boom of a backfire) out the 2 into 1 V&H Pro-pipe. Then after letting the scoot sit & cool off, after attempting to start it & experiencing the above characteristics, it would fire right up like nothing was wrong ! And during ALL of this, over a period of 15K miles, the engine would ALWAYS run beautiful as I was riding ! I installed HD's Stage-IV kit when the scoot was new, along w/port & polished the original heads. So, I say "new", but the Stage-IV install was after I broke the motor in, around 1500 miles, which was 26K miles ago ! And I ride responsibly, I DO NOT abuse my scoots. This "issue" has been taking place now for approx'y the last 10K-15K miles. Which = Approx'y 2-summer riding seasons. I put approx'y 7K-9K miles on it per summer/year. I've been building, customizing & wrenchin' on scoots for a few decades....too many to want to remember really. Ha ! So I'm very familiar & knowledgeable w/anything Mechanical/Electrical. I've already gone through the starting system, and the ACR system. Both check out to be normally operable. The Compensator is original OEM, which is the new SE design, and "seems" to be operable & not making any noise. (But that doesn't mean its not a bad Compensator) The CPS is "Good". Another friend of mine is a High-Performance engine builder for a Dealership down in Newburgh, NY. If I cant pin-point this hard-start issue, I'm taking my scoot to him. It's either a timing issue, and/or an intake leak possibly....or a fuel pump issue ! So I'm going to check my compression, Hot & Cold. Then check the intake for a leak (w/LP), and remove all the EFI in the tank, and check the pump pressure. Unbelievable ! So if ANYONE has had a familiar issue, please shoot any info my way, I'd be very grateful. Thank you so very much guys !
 
Great description on your bike and the problem. I'm hoping someone will come up with a solution to your issue. Keep us posted on your progress, this type of post will really help all of us once it is sorted out. Thanks, Don
 
This is just a thought.
The fuel pump can make pressure, and it is in specs, but what about volume, may be a restricted fuel filter causing a lean condition. The milage on your bike is close to what I had on a RKC that was doing what yours is but also a decel backfire. After replacing the filter both problems went away.
 
The not starting when hot sounds like what we called heat soaked, it could be a combo of compression, too much fuel, leaky intake and weak starter, just to be sure here the SE compensator could be going south also
 
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