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Old 05-27-2018, 10:57 AM
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agirard7a agirard7a is offline
 
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Location: Newport, RI
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Default Carburetor jet size

I have an 0320 that I upgraded from 150 hp to 160 hp. I am running lean on climb out and seeing high temps on CHT (over 400) and EGT. (1,300 plus). Fuel flow at 90-95% power is 11gph. Lycoming manual states it should be high 12-13 gph.

I would like to drill out the jet to the next numbered drill size. I have included a photo bellow. What part number actually gets drilled out? Is it the very tip of the nozzle( 1 ) or is it part which is listed as the power jet (4) that appears to look like a gasket. Does the lower part of the nozzle come apart to expose the jet?

For those who have done this, I would love some feed back. Thanks.


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  #2  
Old 05-27-2018, 11:41 AM
YellowJacket RV9 YellowJacket RV9 is offline
 
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Location: Clearwater, FL / KZPH
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It is part #1. One end of it is restricted, and you just drill out that small section. I have done it twice, in two small increments, to get to where I felt happy. First time under the direction of a professional aircraft carb rebuilder, the 2nd time myself. Really not too complicated. Just make sure you buy new replacement gaskets / lock washers for everything that comes apart.

To make sure the hole was drilled perfectly I made a jig to hold the nozzle under a drill press. It is soft metal and drills easily.

Chris
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  #3  
Old 05-27-2018, 01:03 PM
Dreamin9 Dreamin9 is offline
 
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Location: Near Buffalo, NY
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I believe, according to the Lycoming power/FF charts, FF at full power (sea level) should be high 13's for the O-320 160.

Recently I was showing 11.6 gph. Jesse Saint changed the jet size from a 42 to 40. I now burn about 12.7 at full power and it still runs a bit hot, may take it up another notch.

It's my understanding that the diameter of the fuel jet is only relevant at or near full power. At partial power, the mixture control (red knob) is what matters.

Carl
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  #4  
Old 05-27-2018, 01:46 PM
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agirard7a agirard7a is offline
 
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Awesome thanks. Just the info I was hoping for.
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  #5  
Old 05-27-2018, 01:52 PM
jabarr jabarr is offline
 
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Location: Fayetteville, Georgia
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Factory max fuel flow numbers are only for full power/ redline RPM (as stated above). You will not achieve full power/rpm with the fixed pitch prop on takeoff therefore fuel flow numbers will be lower.
You can find a more accurate flow number based on your actual rpm/map if you can decipher the Lycoming charts.

Last edited by jabarr : 05-27-2018 at 02:07 PM.
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  #6  
Old 05-27-2018, 02:03 PM
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snopercod snopercod is offline
 
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An old machinist trick: When drilling brass, round off the corners of the drill bit with a stone. That keeps the bit from "grabbing". That's what I did when I drilled out the nozzle in my MA-3SPA. Mine was the same inner diameter all the way through.
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