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Os ax .46

Old 09-20-2021, 08:17 AM
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stearman70
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Default Os ax .46

Hello. I'm not a newcomer to the hobby but I have a problem with an OS AX .46 engine. He was riding a plane and worked excellently well. I disassembled it to clean and wash it, put it together and put it back on and I haven't been able to carburete it at low speed. I closed the idle screw completely and began to open it little by little (1/8 turn each time), the engine works excellent from intermediate to high speed, but when the accelerator goes down more, it turns off. Is there a secret I don't know to let him work well again? Sending photo with the position of the idle screw. Thanks in advance.

This is idle screw.
Old 09-20-2021, 10:22 AM
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Did you put it back together correctly?
Old 09-20-2021, 10:41 AM
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Originally Posted by HansenTsang View Post
Did you put it back together correctly?
Yes, I putted all things OK. I think that trouble is in the idle screw's calibration.
Old 09-20-2021, 10:53 AM
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Originally Posted by stearman70 View Post
Yes, I putted all things OK. I think that trouble is in the idle screw's calibration.
Ok, in my experience if I put an engine back correctly the idle mixture will not change much. Unless of course you have change the idle screw position when you took it apart. The best way for me to check the idle screw adjustment is by trial and error and I use the "pinch the fuel line" method.

I adjust the idle mixture screw to an approximate position. I use a tachometer and run the engine. Get the high end adjusted approximately. Then lower throttle lever slowly and listen to the engine and watch the tachometer. When you get to a fairly low RPM, hold it and pinch the fuel line. If the engine speeds up for a long time your idle is too rich. Close the idle screw by 1/4 turn and try again. If adjusted properly the engine should speed up just a little bit (300 to 400 rpm) and die. If the engine quit before speeding up your idle screw is too far in.

If adjusting the idle screw does not change the low speed behavior of your engine idle then you did not put the engine back together correctly or there are other issues with your engine. Most likely a lack of compression or bad bearings.
Old 09-20-2021, 11:01 AM
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Originally Posted by HansenTsang View Post
Ok, in my experience if I put an engine back correctly the idle mixture will not change much. Unless of course you have change the idle screw position when you took it apart. The best way for me to check the idle screw adjustment is by trial and error and I use the "pinch the fuel line" method.

I adjust the idle mixture screw to an approximate position. I use a tachometer and run the engine. Get the high end adjusted approximately. Then lower throttle lever slowly and listen to the engine and watch the tachometer. When you get to a fairly low RPM, hold it and pinch the fuel line. If the engine speeds up for a long time your idle is too rich. Close the idle screw by 1/4 turn and try again. If adjusted properly the engine should speed up just a little bit (300 to 400 rpm) and die. If the engine quit before speeding up your idle screw is too far in.

If adjusting the idle screw does not change the low speed behavior of your engine idle then you did not put the engine back together correctly or there are other issues with your engine. Most likely a lack of compression or bad bearings.
There is no way to put the engine parts together badly. The problem was presented yesterday on the airfield. In this week I will try to correct the fault in my workshop. I will let you know of the results. Thank you for your information.
Old 09-20-2021, 11:05 AM
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Originally Posted by stearman70 View Post
There is no way to put the engine parts together badly. The problem was presented yesterday on the airfield. In this week I will try to correct the fault in my workshop. I will let you know of the results. Thank you for your information.
Maybe the engine was running well because the piston to cylinder sleeve seal was good from old oil. You cleaning the piston and sleeve may have reduce the compression. Check the idle screw adjustment first and hopefully you can get the idle back. Otherwise compression is the biggest issue regarding a poor idle.
Old 09-20-2021, 02:06 PM
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Originally Posted by HansenTsang View Post
Maybe the engine was running well because the piston to cylinder sleeve seal was good from old oil. You cleaning the piston and sleeve may have reduce the compression. Check the idle screw adjustment first and hopefully you can get the idle back. Otherwise compression is the biggest issue regarding a poor idle.
.
I still think that the problem is the sprea, since when I washed the engine I only removed the carburetor and the rest I did it on the outside without removing even the spark plug. Thank you again.
Old 09-20-2021, 03:20 PM
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Piston seal is what will affect the idle quality/ability, not compression. The better the piston fit at the bottom of the stroke, the better. Usually a worn out piston fit will cause a poor idle. Look for peeled plating in the cylinder liner’s bore.
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Old 09-22-2021, 01:58 AM
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Hi!
Could be that you have set the idle screw too rich.
What happens when you have started the engine (at idle) and give full power? Does the engine sputter and die or just die? If it sputters an hesitates the idle needle set too rich.
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