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Jul 10th, 2007, 10:01 AM
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#1 | | Newbie
Join Date: Apr 2007
Posts: 5
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I keep getting a backfire out my carb while downshifting, happens about 50% of the time. I have put on Screamin' Eagle slip-on mufflers, Stage 1 carb kit, S & S air filter kit and new exhaust gaskets. WTF??? When I re-jetted the carb, I turned the mixture screw in as far as it would go and the engine never stumbled, maybe my idle jet is too big? | 
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Jul 10th, 2007, 11:03 AM
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#2 | | Administrator Frequent Posting Club
Join Date: Jan 2005
Posts: 1,214 Model: Harley FLHX Occupation: Web Developer by day, 25+ years of carb building by day, hey what happened to my day?!
| If the idle jet were too large it wouldn't necessarily cause a decel pop back through the carburetor, and on Twin Cams the mixture adjustment doesn't always stumble when turned it in. Your idle jet should probably be a #48 with the mixture screw set at around 2 or 2-1/4 turns out. If your idle jet is too large you should be seeing fouled plugs.
Also check to make sure you have a good seal between your slip-on mufflers and pipes, since cool air drawn back in will cause popping. | |
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Jul 27th, 2007, 05:08 AM
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#3 | | Newbie
Join Date: Apr 2007
Posts: 5
| Thanks for the tip! I did as suggested and it did help but the bike is still coughing through the carb just not as often maybe 10% of the time now. I pulled the plugs and the electrode and terminal are a nice tan color but the base of the threads are sooty. I need to go by the electrode right??
I am also going to need my 10,000 mile check-up. Anybody know of a good mechanic in central New Hampshire? | |
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Jul 28th, 2007, 08:22 PM
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#4 | | 200+ posts and climbing
Join Date: Oct 2005 Location: West Texas
Posts: 306 Model: '68 FLH, '99FB,'02 RK Interests: riding,custom paint, pinstriping. Occupation: retired
| One way I check for an exhaust leak is to put the bike in my shop and turn the lights off (obviously don't let it run more than a few seconds without ventilation). You can literally see the exhaust leak. You will see fire coming out at the seal. Some folks spray carb cleaner on the seal and listen for an rpm change but for me seeing is believing.
Which leads me to a story. Back in the '80's i was coming down the divide on my Shovel heading into Berdoo and blowing blue flames out the pipe (drags with no baffle) and I got wrote up for being a "fire hazard". I still have the warning citation in one of my scrap books. Been called a lot of things but that was a first. Al | |
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Jul 30th, 2007, 08:01 AM
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#5 | | More than 100 posts!
Join Date: Dec 2006 Location: Cape Coral, Florida
Posts: 124 Model: '04 FXDL Interests: drag racing, muscle cars, street rods, annoying others
| Spraying the carb cleaner around seals is for finding a intake leak, not exhaust. Maybe you are a fire hazard! LOL : ) | |
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