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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 26th August 2009
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Default All of a sudden ... pop, pop, popping

Last weekend a buddy and I went for a ride in the mountains. He bought an '02 1200S about the same time as I totaled my last bike and this was the first chance we've ever had to ride together (he's been lurking around here and I'm trying to get him to become a member). Mine is an '03 1200C with 10K miles that has run great for the first 300 miles that I've owned it.

After putting on about 100 miles I noticed that my bike was suddenly popping when decelerating. Now it does it all the time. Every time I let off the throttle it pops and pops and pops until I pull the clutch. Everything else seems to be the same: it starts right up, idles nicely, and seems to have plenty of power. But something has changed/moved/shifted because it hasn't had this problem since I bought it. She has a ThunderHeader 2:1 exhaust, stock carb with a Thunderslider and a Screaming Eagle air cleaner.

Any suggestions on where I should start looking for the cause? Could this be something as simple as loose connections at the manifold?
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Old 26th August 2009
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Hmmm, I may have found my problem. When I installed my Pingel petcock, as with any non-vacuum petcock, I plugged the line to the carb. I just noticed that the plug is gone and the line that used to go between the stock petcock and the carb is open.

Could that be my issue (can't test this until the engine cools a bit)?
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Old 26th August 2009
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Check your exhaust bolts they are probably loose. It sounds like an exhaust leak to me.
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Old 26th August 2009
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mine did that I foudn one of my exhaust bolts missing got a new one put some hifgh temp loctite no more problems
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Old 26th August 2009
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The missing plug is causing a vacuum leak. A lean mixture can cause your popping.
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Old 26th August 2009
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Is it hot where you ride? It was 107F today. How's it jetted?
Usually a gasket leak will cause the decel pops. The following items affect how the carb works:
Altitude.
Temperature.
Humidity.
Riding Style.
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Old 26th August 2009
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Quote:
Originally Posted by wilbur View Post
Is it hot where you ride? It was 107F today. How's it jetted?
It's typically mid-90's to 105 this time of year but it's been that since I bought the bike. The bike is relatively new to me and I don't know how it's jetted – only that it was re-jetted when the previous owner added the ThunderHeaders.

I'm going to close off that vacuum leak to the carb (this time with something more permanent) and take a wrench to my exhaust bolts. Hopefully it's something simple like that.

Thanks all.
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Old 26th August 2009
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I belive plugging that vacuum leak will solve your problem. It's running LEAN with that baby sucking in all that air!
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Old 26th August 2009
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Popping through the carb on accel is lean. Popping through the exhaust on decel is almost certainly an exhaust leak. Check for flange leaks, joint leaks, or a cracked collector on the Thunderheader.

I bought my Thunderheader because a craked stock pipe was causing pops and backfire on decel. I welded it twice and it broke again just past the weld.
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Old 26th August 2009
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Quote:
Originally Posted by chris_lacey View Post
Popping through the exhaust on decel is almost certainly an exhaust leak.
Chris.......I know when I was tuning my Mikuni and had de-cel backfires through the exhaust...it was too lean on the pilot....because the throttle was closed and it was just running on the pilot.

I think the Mikuni tuning manual even mentions that de-cel backfiring can be caused by a lean condition.
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