Method for mixture valve/idle adjustment
06-25-2004, 11:25 AM
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Method for mixture valve/idle adjustment
Found the following article on Model Sport Aviator
http://www.masportaviator.com/ah.asp?ID=41&Index=0
It presents a technique for idle adjustment I had not heard of and seemed to be a little more precise than watching the transition from idle to WOT.
I have been holding off full power needle valve adjustment until I had broken in my engine some. I might try this next time I'm at the field. I have not been able to get my idle much below 3000. According to this method, my problem is likely that my mixture valve is still too rich. (The engine loads up and stops below a certain RPM that is higher than the 2400 RPM target laid out in the article).
http://www.masportaviator.com/ah.asp?ID=41&Index=0
It presents a technique for idle adjustment I had not heard of and seemed to be a little more precise than watching the transition from idle to WOT.
I have been holding off full power needle valve adjustment until I had broken in my engine some. I might try this next time I'm at the field. I have not been able to get my idle much below 3000. According to this method, my problem is likely that my mixture valve is still too rich. (The engine loads up and stops below a certain RPM that is higher than the 2400 RPM target laid out in the article).
06-25-2004, 08:20 PM
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RE: Method for mixture valve/idle adjustment
2400 is a catch all number. Some engines will idle loer some will not. The big thing is prop size. A big lond diameter prop will want to idle lower. In fact it will have too. The pull from a long prop may not let the plane sit still at idle. By the same token a small diameter high pitch prop wpould idle higher. I never worry about idle speed. I never use a tach. Just set it up so it idles good and will sit still. Set the top end so it is slightly rich. Make sure the transition is good. Then fly the snot out of it.
It sounds like your low speed needle is too rich. Lean it out slightly and try it. The diagram would work ok for setting the high speed needle only. It assumes your low speed is fine. Good luck with the engine.
Mark Shuman
It sounds like your low speed needle is too rich. Lean it out slightly and try it. The diagram would work ok for setting the high speed needle only. It assumes your low speed is fine. Good luck with the engine.
Mark Shuman
06-26-2004, 12:58 AM
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RE: Method for mixture valve/idle adjustment
I know that I have a good idle when I can put my plane on JUST REDONE ASPHALT, and the darn thing won't move....My Sig Somethin' Extra with an APC 11x6 prop on a OS 46AX won't move unless I make it. I switched to a wood top flight prop (I like the throttle response from the wood kind) but I haven't been out on that road to try that out seeing if that won't move....
There is a thing on [link=http://www.airfieldmodels.com]www.airfieldmodels.com[/link] (I forgot the guy that made it; who is someone in RCU) that was saying that it's the opposite of richen (in).....it you want to lean it, you turn clockwise......It would be better if you wanted to richen the mixture, you would screw in.....but that's not the case
There is a thing on [link=http://www.airfieldmodels.com]www.airfieldmodels.com[/link] (I forgot the guy that made it; who is someone in RCU) that was saying that it's the opposite of richen (in).....it you want to lean it, you turn clockwise......It would be better if you wanted to richen the mixture, you would screw in.....but that's not the case
06-26-2004, 12:08 PM
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RE: Method for mixture valve/idle adjustment
Maybe it varies, but the following is from my OS 50 SX manual, Page 23
With the engine running, close the throttle and allow it to idle for about five seconds, then open the throttle fully. If, at this point, the engine is slow to pick up and produces an excess of exhaust smoke, the mixture is too rich. Correct this condition by turning the Mixture Control Screw clockwise 15-30°. If the mixture is excessively rich, engine rpm will become unstable: opening the throttle will produce a great deal of smoke and rpm may drop suddenly or the engine may stop. This condition may also be initiated by excessively prolonged idling.
If,on the other hand, the mixture is too lean, this will be indicated by a marked lack of exhaust smoke and a tendency for the engine to cut out when the throttle is opened. In this case, turn the Mixture Control Screw counter-clockwise 90°to positively enrich the idle mixture, then turn the screw clockwise gradually until the engine regains full power cleanly when the throttle is reopened.
Carry out adjustments patiently until the engine responds quickly and positively to the throttle control.
If,on the other hand, the mixture is too lean, this will be indicated by a marked lack of exhaust smoke and a tendency for the engine to cut out when the throttle is opened. In this case, turn the Mixture Control Screw counter-clockwise 90°to positively enrich the idle mixture, then turn the screw clockwise gradually until the engine regains full power cleanly when the throttle is reopened.
Carry out adjustments patiently until the engine responds quickly and positively to the throttle control.
