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  #11  
Old 09-13-2018, 08:06 AM
lr172 lr172 is offline
 
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Originally Posted by hcccs View Post
If it were too lean would it run well at higher revs. Mine does so I wonder.
I said your "idle mixture" was too lean. Your idle mixture screw only sets the mixture for low RPM operation, up to about 1000-1200 RPM. After this, your mixture is controlled by the main circuit (no adjustment other than main jet size). One has nothing to do with the other and are not related, except in the RPM range where control is transitioning from the idle circuit to the main circuit.

Larry
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  #12  
Old 09-13-2018, 03:02 PM
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hcccs hcccs is offline
 
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Originally Posted by moosepileit View Post
The blueish plate between the carb, gaskets and sump- is that leakfree? Can you check for induction leaks with egts on each cylinder? The lighter prop is more revealing of any issues at idle.

Which part number carb? Is it new or newly overhauled?

The carb number is 10-5009 which is the one to use for O320-E3D. I took it apart and cleaned it before installing it. I don't know yet what jet is installed.
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  #13  
Old 11-04-2018, 02:35 PM
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hcccs hcccs is offline
 
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Back again with my rough idling O320. I took the carb apart and tested the idle passages and fuel passed through. A mechanic told me to turn the mixture screw out 4 turns and start testing from there. I did so and the rpm went up 50 when leaning, just as it should, but it ran as bad as before at 600-650 rpm. I even tried 4½ turns. Now I read something in a document from Kelly Aerospace: "An idle adjustment screw that requires more than four turns out to achieve a proper mixture rise at ICO is a good indication of contamination in the idle circuit." Maybe there is some contamination in the idles mixture passages after all. How do I clean them, ultrasonically or with some other means?
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  #14  
Old 11-04-2018, 06:35 PM
dougnlina dougnlina is offline
 
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If the cylinders/rings are new and the engine is not broken in, it might take some hours on the jugs for the idle to smooth out when idling as low as 700-
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  #15  
Old 11-05-2018, 02:07 AM
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Originally Posted by dougnlina View Post
If the cylinders/rings are new and the engine is not broken in, it might take some hours on the jugs for the idle to smooth out when idling as low as 700-
The Millennium cylinders all have 700 hours since new.
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  #16  
Old 02-04-2019, 02:01 PM
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Originally Posted by fixnflyguy View Post
I am running an O-320H2AD/1600 hp with a Sterba wood prop, and idle at 600-650 is rough. I have it set for that only to allow me to throttle way back, but I keep my idle around 800 RPM on ground to be happy. There is little similarity between an O-320 and a C65-C90 which will purr at low idle with a wood prop. There just isn't enough inertia/weight in a wood prop for the low idle on the O-320

Removed the magnetos, changed one faulty coil and the engine runs a little better but not much. What difference could there be between a C90 and a O320? O-320 has 50% more cylinder volume but both have a compression ratio of of 7:1 so where else is it different?
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  #17  
Old 02-05-2019, 06:17 AM
fixnflyguy fixnflyguy is offline
 
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You just said it..50% more volume..Its just plane old math. Prop size/weight isn't much different,compression ratio is just the math multiplication factor for volume, but the amount of air compressed is much more.
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  #18  
Old 02-05-2019, 06:50 AM
mahlon_r mahlon_r is offline
 
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Hey Hans, Long time since we talked. Hope you are well.
Some basic things to check.
Make sure the carb air temp hole in the carb is plugged.
Make sure all of the 1/8 pipe plugs, where a primmer fitting or FI nozzle would go in the cylinders, are all there.
If you have any sort of primmer system installed disconnect it as close to the engine side as possible, block it off on the engine side, and try running with the primmer system removed.
Screw the isle mixture screw adjustment all the way in and back it out 11/2 to 2 turns.
Good Luck,
Mahlon
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  #19  
Old 02-05-2019, 09:14 AM
Finley Atherton Finley Atherton is offline
 
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Originally Posted by hcccs View Post
I can't even decide if it is running too rich or too lean.
I presume you checked for correct idle mixture adjustment at a higher idle rpm where it was running OK. If so try pulling the mixture full out to idle cutoff when it is “misfiring” at low rpm. If the misfire ceases and it revs up considerably before the engine stops then it is likely too rich.

If it does seem too rich then the next step would be to check the actual fuel level in the carb bowl. Remove the carb bowl drain plug and make a temporary replacement plug such as a barbed fitting with a clear plastic tube attached and route it vertically to above the carb. Directly observe the fuel level which should be somewhere below the level of the main gasket. (reinstall the plug before flight!!)

Fin
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Last edited by Finley Atherton : 02-05-2019 at 10:12 AM.
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  #20  
Old 02-05-2019, 12:09 PM
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snopercod snopercod is offline
 
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I have an O-290-D2 which is pretty much like an O-320 only with an MA-3SPA carb. Mine will idle down to 500 RPM with a wood prop. Looking at the Marvel Schebler troubleshooting guide for rough idle, induction leaks and primer leaks are two of the top suspects. Also, that hole in the carb barrel above the Throttle Fly is (I think) the "Primary Idle Delivery". This is the one controlled by the big Idle Adjusting knob mentioned earlier. Just under the Fly are the Secondary and Third Idle Delivery holes. There are lots of good diagrams here: http://www.insightavionics.com/pdf%2...b%20Manual.pdf
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