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Warm start backfire 883

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  #1  
Old 05-29-2018, 10:34 AM
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Harleydarley
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Default Warm start backfire 883

Hi all,

I have a 2000 883 carburator. When the bike is cold it starts with choke and 3 throttle blibs. It always starrsperfesta when it is cold. It also always drives like a dream (cold and warm).

However when the engine is warmed up and I shut it off for approx. 30 minutes it often wont start. After cranking for 5 seconds you often hear the sound of a shotgun coming out of the exhaust.. It wont start until I flip the killswitch a couple of times and then press the starterbutton shortly. Often I have to repeat this proces 10 times or do before it it starts.

The bike does start if you shut it off for only 5 minutes or so.

things i have already checked:
- spark is always there. Blue/purple color.
- carburator is ultrasonic cleaned (170 main jet, 44 slow jet, 2.5 turns mixture screw).
- vacuum lines replaced

Things i replaced:
- coil
- swapped ignition module
- new spark plugs and wires
- battery is 100%

Maybe I have missed something. Does someone has an idea?
 
  #2  
Old 05-29-2018, 02:34 PM
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what pipe are you using? it helps to know if you are in the ballpark on your jetting. have you checked it for vacum leaks at the intake seals and everywhere else?
m
 
  #3  
Old 05-29-2018, 03:11 PM
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Forgot to mention the intake seals are new.

Stock airfilter
Open pipes (unbranded)
 
  #4  
Old 05-29-2018, 09:07 PM
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have you checked the venting for the gas tank,,,IIRC sportys vent through the gas cap, maybe a heat soak/vapor lock type thing. make sure that your tank is venting properly. did you check for vacum leaks on the vacum hoses to the voes and the petcock? maybe loose or cracked?
m
 
  #5  
Old 05-29-2018, 11:59 PM
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Yes I did check all of that. It makes no difference if I let the fuel cap open but thanks for the suggestion !
 
  #6  
Old 05-30-2018, 07:16 AM
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Have you checked the battery voltage when the bike is hot and giving you the hard time? THIS IS ACTUALLY an issue that i experience on one of my own built motor xl's when the battery is beginning to fail. Check and make sure your voltage during cranking is not dropping below 10 volts.
m
 
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