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Sportster Motorcycle Air intake, Carburetor, EFI, Fuel, and Exhaust Problems, advice and/or how tos for Sporster and Buell motorcycle carburators, Electronic Fuel Injection (EFI), Air Intake, Fuel and Exhaust.

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  #1  
Old 14th January 2019
jhead013 jhead013 is offline
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Default 2009 Nightster Pop through intake

On a cold start on my 09 Nightster 1200, if i give it any gas before it gets warm good it will lose power for a split second and pop through my intake. I am guessing it is a backfire but not 100% sure. Any help on diagnosis would be nice. I have checked for intake leaks and have not found any, nor do i have any DTC's that i know of. Bike has 7500 miles.
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  #2  
Old 14th January 2019
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Check your intake seals.
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  #3  
Old 14th January 2019
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Quote:
Originally Posted by Folkie View Post
Check your intake seals.
Which may fix the overly lean condition.
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Quote:
Originally Posted by Folkie View Post
Check your intake seals.
Here's how:
Intake And Exhaust Leaks Tests

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  #5  
Old 14th January 2019
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Default

I have checked for an intake leak before but could not find one. I will double check myself tonight. Would MAP gas work any better than propane? Also do you all think it could possibly be an injector? I had a friend tell me it could possibly be an injector causing a lean condition. Any idea on how to test an injector at home?
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  #6  
Old 14th January 2019
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Some thoughts.

1) Collapsed lifter on exhaust, exhaust doesn't open, so it pops back out the intake. It was more common on older bikes where the adjustment backed off on an exhaust valve. (Found it on a Shovelhead a few years ago).

2) Intake valve burnt / hanging (sticking) open.

3) That's actually normal for a carbureted bike before it warms up, which goes along with the possibility of it being lean.

4) Worn out cam lobe on exhaust. (had this on a 69 Camaro many years ago).
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Old 15th January 2019
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i had a similar problem a couple of years back. didn't find any leaks either. took down the manifold to be sure and found a crack on the intake flange. replaced them and the seals and it was fixed.. i couldn't duplicate the effect at idle...

if it were my bike, i'd replace the seals , They're 10 years old at least and it's not an expensive solution.
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Old 15th January 2019
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Lean mis-fire is likely cause
Colder plugs "might" fix it
Tighten up the plug gaps to .035
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Default

Quote:
Originally Posted by ReddTigger View Post
...if it were my bike, i'd replace the seals , They're 10 years old at least and it's not an expensive solution.
Good advice. Worth doing even if it is not the current issue.
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