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Carb Cough

If the issue only occurs when cool and wet temp below 15c and humidity 75% or above then it will be carb icing
the moisture in the air is chilled by the way it is drawn through the carb further chilling occurs when fuel atomises this makes for a very cold zone in the carb the moisture in the air freezes at the coldest points usually the jets as there is a needle in the main jet it will stay clear as the needle moves up and down but the ice will block the slow jet creating a very lean condition at lower speeds
once the bike is fully warm there is enough heat being generated by the engine to radiate and melt the ice as it forms
The design of the carb is the main problem here i personally got the same issue with both my big twins
Fuel additives may help but i replaced the carb on both big twins with a mikuni hsr 42 then no more problems

Brian
 
Take it from a licensed Airframe and Powerplant mechanic (carb icing is one of the first things you learn about in Powerplant school)...

Fuel additives are not going to help. The icing has nothing to do with the fuel, it is caused by the cold air in the carb freezing the moisture that is in the air.

The only cure is to raise the temperature in the inlet.
 
Thanks FLST89 and Fin676,
I have experienced carb icing in my car a few times, and in my airplanes(yes I am a pilot).
I haven't ruled that out. However, while driving 16 hours from Las Vegas to Vancouver, BC in June the bike never missed once until I reached Idaho with the cooler temps and damper air. Then all the way home to Vancouver the occasional miss in the 1st quarter throttle positions on a fully hot engine that had run all day. Before I replace the carb because of icing problems I am trying tuning adjustments.
Today I started in warm dry Vancouver and drove up to the cool mountains. It did not miss at all until I got up to 500 meters or so and temps near 18C with the bike fully warmed up by then. Idle mix was 2.25 turns out. I don't know what the dew point was but there were no clouds in the air so I will gamble it wasn't icing.
So if it's too lean in low temps what is the tuning solution?
I tried the idle mix screw in and out and left it at 2 turns open. No missing after that on the way down the mountain but the air was getting warmer. Some minor decel popping not really worth mentioning.
Do bikes sold in the Pacific Northwest have specific tuning requirements different to other Harleys destined for other markets or are all FXDLs tuned the same?
 
As far as i am aware all bikes coming out of the factory would have been pretty much the same with the exception of the California models which required to pass more stringent emission requirements
As i live in a cool damp climate i have in the past experienced similar issues to yourself and the carb replacement was the only thing that worked for me however i have only experience the issue once or twice at warmer temps and stop bike let it sit for a short time allowed the heat to penetrate then it would work well
It did seem to be more of an issue with the stock air cleaner than with the se however it is hard to remember specifics 6 years on

Brian
 
Just rode all day in hot dry air (24C). No coughing with mixture screw at 2.25 out, one #4 washer, idle at 1000, 48 pilot and 190 main. The weather is not cooperating. It was a great ride though. I will have to wait for the cooler wetter days to get a cough and tune it out if possible. At least it isn't coughing now and that's good. I will post again this season if necessary.

Thanks to all who contributed to this thread.
 
i have an 05 fxstb with a 48 & 195 and 2 washers ,screw out at 2 5/8 .she runs strong but every now and then she snorts being that she is a pig. but if you look around when she does it ,there is something there she is pointing out to me . just ask Bodeen
 
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