Question about 2004 Harley Davidson FXDX - FXDXI Dyna Super Glide Sport

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2005 carbie starts but misses and backfires at 2000 rpm. It has an Arlen ness stage 1 kit and the jetting may be a little out . It has new plugs and a clean airfilter

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Did the kit come with a new needle? It sounds like it's a little lean in the mid-range. I'd pull the slide out and take the needle out of the slide. From the long end of the needle, slide a 3mm flat washer up onto the needle. Use a small dab of grease to hold it on the needle while you put it back in the slide. The small washer should be about 0.020"-0.025" thick. This will RAISE the needle just slightly enriching the mixture just a bit in the mid-range. It will not change your idle setting nor the wide open throttle jetting.

Good Luck

Posted on Sep 09, 2010


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Haveing (carb farts)spitting and backfire from carburetor on 2001 1200 harley sporster.what is causing it and what can i do?

1. First check you carburetor manifolds for intake leak warm the engine up and spray WD40 all around the where the manifold connects to the heads if the rpms change when you do thins you have leak replace the gaskets.
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Jun 04, 2010 | 2000 Harley Davidson XL 1200 C Sportster...

1 Answer

Had a 1200 upgrade, new exhaust valves, guides seals, have a stage 1 arlen ness filter, 2 1/2 " 45 calaber drags, had a 45 slow jet, the shop put in a 170 main jet, ran fine for a while then the plugs...

I would say that something has changed since you had the work done. You said that it ran good and got 54 mpg (you said "mph" but I think you meant MPG") after the work was done. Now, it's backfireing, sputtering, and getting 37 mpg with dry black deposits on the plugs. Something has changed.

Considering that you didn't mention anything you changed, the only thing that has changed is the weather, it has turned cold. Cold air is more dense than hot air therefore, your carb should be running leaner, not richer. But, I'd be willing to bet that you're allowing your bike to run longer with the enricher on when warming it up before a ride. Am I right?

The enricher circuit is a very rich mixture. It's rich enough that if you allow your engine to run too long with the enricher on, it will foul your plugs. Fouled plugs are indicated by a black sooty deposit on them. In my experience, once a Sportster fouls a plug, it will not clean itself like a Big Twin will. Why this is I have no idea but that's my experience. You'll either have to replace the plugs or get them cleaned somewhere. I clean them in a glass beading machine but you have to blow them out very well before reinstalling them. I also put a little anti-seize on the threads to keep from damaging the spark plug hole threads.

Try installing a new set of plugs and when you start your bike, only run the enricher long enough to warm the bike to the point where you can keep it running with the throttle lock knob to bring the engine to operating temperature. That enricher is a plug killer.

The only other thing I can figure is that the main jet has come loose and fallen out, trash in the needle and seat, a vacuum leak on the front head at the intake manifold, the VOES, or petcock. If it ran good in warm weather with the 170 main, it should run good or may a tad lean in cold weather.

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