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Discussion Starter · #1 ·
When I run up in the rpms if pulls fine but when I let off it is constantly popping and backfires. Would this be more from my needle position, or air fuel or the jets? It is also a little difficult to get started when its cold. No redness to pipes so idk if its lean or not
 

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List any modifications you have, as well as elavation, as that changes what carb settings and jets are needed.
Incorrect carb settings can cause hard starts, but so can tight valves, so check the valves and adjust if needed too.
 

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Discussion Starter · #3 ·
It has full Fatboy 4 exhaust by Duncan Racing, K and N filter with open air box, and Dyno jet kit. I'm in Pensacola Florida so I'm at a low elevation. The work was done in North Georgia so I'm wondering if the elevation change is causing it. The needles are both on the 5th setting out of 6 and I'm pulling it apart now to see what size jets are in it. I also am gonna adjust the valves while I'm in it. But I'm lost on the carb settings and how to adjust them for what it needs.
 

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Discussion Starter · #4 ·
The jet sizes were 144 and 146 with the needles on number 5 out of 6. I called dynojet and they said both needles need to be on number 4 and air fuel needs to be 3 turns out from bottom. Does this sound pretty close?
 

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The jet sizes were 144 and 146 with the needles on number 5 out of 6. I called dynojet and they said both needles need to be on number 4 and air fuel needs to be 3 turns out from bottom. Does this sound pretty close?
Yeah, both air screws should be set the same, and 2.5 to 3 turns counter clockwise.
Needles in 3rd or 4th, not 5th or 6.
146/148 mains sound good, and could go to 148/150(right main jet will always be one size higher than the left, all other carb settings will be the same on both carbs).
You also Need #25 or #27.5 pilot jets in both carbs, no way around it with open airbox.
#22.5 pilots are stock.
If you need the pilots
www.jetsrus.com
You can check/set the float heigth with the 3mm Clear tube method in the 660 Stickie section.
That also shows you how to trim float stops if you have high rpm fuel starvation issues.
 

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Discussion Starter · #6 ·
Ok thanks that is right on the money then. But I just set my valves as well and it fired up for just a second and spit and sputtered really bad. It coughed out a huge cloud of white smoke through the air filter..... idk what that means or how to fix it....
 

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Ok thanks that is right on the money then. But I just set my valves as well and it fired up for just a second and spit and sputtered really bad. It coughed out a huge cloud of white smoke through the air filter..... idk what that means or how to fix it....
Are you sure you set them on the correct stroke?
If the valves are not sealing correctly it will backfire through the carbs.
 

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Discussion Starter · #12 ·
27.5 pilot and I may have adjusted them on the wrong stroke.... when I started they wasn't even room for my smallest gauge. I think it was .002, paper thin
 

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Discussion Starter · #13 ·
Ok so after I re adjusted the valves, it idels great and sounded like it reved smooth, but after just a min of running the header pipe was glowing red. I am at the 4th out of 6 needle position, 144 and 146 jets with 27.5 mains and 3 turns out each. Yes all the jets and carb is clean as can be. The carb was rebuilt about 3 weeks ago and jet kit was installed by a professional. Idk how it's still lean but should I move my clip back to 5? Or come out another turn on the air fuel or what?
 

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Is the airbox open?
 

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So, with your airbox and exhaust, I'd have installed 146 left, 148 right DJ jets with (MPORTANT!) DJ needles 1 notch rich of center, 25 pilots and fuel screws at around 3 turns out (or 27.5 pilots with screws around 2 turns)...

Popping on decel is usually due to being a bit lean in the idle (pilot jet and screw) circuit - so turn your screws out a quarter turn each and see if that helps.
 
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