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MARKYSTEW
Samba Member
Joined: August 22, 2009
Posts: 104
Location: UK
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 Posted: Tue Jun 21, 2016 9:44 am Post subject: Judson carb icing |
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I've just finished a 40hp build with a judson and it's suffering from carb icing. Anyone have a fix for this?
Engine spec:
Standard 40hp
28pict with 135 main
ZV PAU 4r5 set at 10 ° tdc
I do not have the oil filler breather connection to the air filter will this help by supplying some heated air?
It also feels like its struggling when I give it some gas like something holding it back? |
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Mr. OGPaint
Samba Member
Joined: September 24, 2010
Posts: 823
Location: Oregon
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| Posted: Tue Jun 21, 2016 5:46 pm Post subject: Re: Judson carb icing |
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Definitely looks like carb ice. Installing a heat riser of some type to the air cleaner will take care of things.
Carb ice is most prevalent in outside air temperatures from freezing upto 70 degrees Fahrenheit (22°C) . In extreme cases upto 90 degrees (32°C) even. Here in Oregon the most common conditions for carb icing are high humidity days in the between high 40s and lmid 50s Fahrenheit (5-14°C)
What is happening is when air goes thru the Venturi the pressure drops (Bernouli's principle). When this pressure drops it causes a temperature drop (Boyles gas law). Humid air then deposits its moisture sort of like precipitation inside the carburetor because cold air cannot hold as much moisture as warmer air. This forms the ice iinside the carburetor throat and on the throttle plate surfaces. Eventually this causes restriction to airflow and movement of the throttle plate. Carburetor ice can form very quickly in some conditions.
The solution is, especially in a Judson, to provide warm air from the engine via an exhaust heat riser to the air cleaner or carb intake
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Patrick Hall |
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