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2004 1200C Off Idle Cough and Backfire

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Old Sep 7th, 2011, 03:33 PM     #1
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2004 1200C Off Idle Cough and Backfire

Hi Guys, new to your forum here... My wife and I own 2 HD's a 2002 Fatboy and a 2004 Sportster 1200C. The problem we are having is in regards to the 1200C. The bike starts up perfectly, idles great and initially runs good at low, medium and hi throttle. The problem is after complete warm up I can't roll off idle. It will idle fine but as soon as I start to roll the throttle is coughes and sputters and backfires very badly. If I jocky the throttle around a bit and get it to catch it will still run good at medium and hi throttle. I have taken the carb apart, completely cleaned every piece and reassembled and problem is exactly the same.
The specs:
*2004 1200C
*HD Air Cleaner Kit
*SamsonUSA "Big Guns" pipes with "Tourque Cones" and Short Baffles
*Added a #45 Slow Jet
*Idle Screw out +- 2-1/4 to 2-1/2 turns
*only 2000 miles
*Fresh Premium 93 Octain Gas
*Just took carb completely apart, cleaned every part and reassembled.

I'm wondering if the bike is just running lean the entire time and then getting too hot??? I've tried searching this problem on line and have had no luck. Hope someone here can help. Yesterday it was somewhat cool at 65* to 66*.
I road this bike for nearly half an hour with no problems, get back home leave it idle in the drive for just a few minuets and it starts acting up???

Thanks in advance for your help.

Brian
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Old Sep 7th, 2011, 05:22 PM     #2
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Re: 2004 1200C Off Idle Cough and Backfire

Sporties are known for the coughing. You may want to try a #46 jet and shim the needle to bring in the main fuel a bit earlier.

Harley Davidson Community (Sportster CV Carb Rejetting)

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Harley Davidson Community (Finding An Intake Leak)

Last edited by glider; Sep 7th, 2011 at 06:12 PM.
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Old Sep 12th, 2011, 09:18 PM     #3
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Re: 2004 1200C Off Idle Cough and Backfire

CPK ....crank position sensor....just changed mine. 31,000 miles. Think yours is part # 32804-04B........about $45 at Zanottis. (check that part # if you get one) The # I gave is for an '05 883.
Good Luck
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Old Sep 24th, 2011, 10:30 AM     #4
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Re: 2004 1200C Off Idle Cough and Backfire

My sons 2005 1200R did the same thing. Here is what we did and it cured the problem:

Under the bottom side of the carb is a small plug (like a freeze plug in an engine), it is about 1/4 inch in diameter. behind the freeze plug is a mixture screw. We removed the plug (and threw it away), turned the screw all the way in (clockwise), only took 1/2 a turn, then screwed it out 2 1/2 turns (counter clockwise). Problem solved.

We were told by a HD mechanic that the carbs are set very lean for California emissions and doing this would richen up the mixture. Worked for us.

Hope this helps.
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Old Sep 24th, 2011, 11:00 AM     #5
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Re: 2004 1200C Off Idle Cough and Backfire

Speaking out of my area of knowledge but do those carbs have accelerator pumps? I know on cage applications, a weak accelerator pump shot will cause an off idle bog (big time).
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Old Sep 24th, 2011, 12:04 PM     #6
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Re: 2004 1200C Off Idle Cough and Backfire

Quote: Originally Posted by Hoople View Post
Speaking out of my area of knowledge but do those carbs have accelerator pumps? I know on cage applications, a weak accelerator pump shot will cause an off idle bog (big time).
Yes the cv fitted to the sportster should have it as part of the carb

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Old Sep 24th, 2011, 12:14 PM     #7
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Re: 2004 1200C Off Idle Cough and Backfire

BikeSag is correct...turning the mixture screw got rid of the "cough"...and Glider's tips on jetting and 2 #4 washers under the needle made my 2004 Sporty run great...(now running short baffles in straight drag 1 3/4" pipes if memory serves with S&S air cleaner. Accelerator pump means you twist throttle a couple time on modest/warm day and you do not even need to use the choke.
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Old Sep 24th, 2011, 01:23 PM     #8
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Re: 2004 1200C Off Idle Cough and Backfire

The later sporties have an accelerator pump while the earlier ones didn't.

Here's some info on jetting...

Harley Davidson Community (Sportster CV Carb Rejetting)
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