Roger Dyke Posted June 4, 2021 Author Share Posted June 4, 2021 Andy: I don't think the clunk would be bottoming out as I always leave a sensible gap when setting up the tank. I think maybe the opposite. I might have answered my own question. After writing the previous post, I decided to empty the tank to put it all away for today. In emptying the tank, very little came out meaning that with the plane in the vertical position the clunk may have been out of the fuel. Got to check that again tomorrow. I was assuming when carrying out my tests that it was still about half full. Tank is impossible to see where it is situated. Nigel: Thanks for the info regarding the idling time. Jon: Thanks for the info regarding nose in the air testing being none-representative. Also the advice for ground idling. Quote Link to comment Share on other sites More sharing options...
Martin McIntosh Posted June 4, 2021 Share Posted June 4, 2021 When I first read this it seemed simple, plugs deteriorate when left in and a poor idle is the first sign. Then there is the bottom end mixture. Richening the top end should have little effect on this. It sounded like the idle mixture is too rich which would give a crankcase fuel build up in a short time. The transition should be instantaneous even on an SC so I would say screw in the idle until the motor hesitates or stops when opening up then richen it gradually until it will snap open. My SC40 2st will idle all day if I want but my 30fs has an idle screw which is too short so I can only get about 30 seconds even if I try 20% nitro (which would require a richer setting). If your motor slows down after a long idle then it is too rich, speeding up indicates too lean. Nothing really to do with a temperature change. Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted June 4, 2021 Share Posted June 4, 2021 2 hours ago, Roger Dyke said: how long should an engine be able to successfully idle for (at about 2800 rpm)? Just a note Roger The model should be difficult to land at 2800 rpm, as it would still be pulling, if the rpm reading is accurate. For braking at idle is best at approx 2000 rpm and 2200 rpm tops Quote Link to comment Share on other sites More sharing options...
Roger Dyke Posted June 4, 2021 Author Share Posted June 4, 2021 Martin: I Think I now have the optimum mixture setting for the idle now. I would not say the transision is instantanious though. I would say bottom to top stick movement of about one and a half seconds is fine with no spluttering or hesitancy at all. Thanks for the info regarding temperature change. Denis: The reason I have 2800 rpm is because I was afraid of it dying if a quick go-around was needed. At the moment our strip is very tight to get in on and resembles a sunken box surrounded by 4 ft high walls of wheat. I know 2800 rpm is a little counterproductive as it's still pulling the model, but several attempts are usually required to get the model in and didn't want to risk a flame-out when hitting the throttle to go around. With the latest adjustments, I think that I may have more confidence in it's reliability. Quote Link to comment Share on other sites More sharing options...
Martin McIntosh Posted June 4, 2021 Share Posted June 4, 2021 Not measured a two stroke motor idle speed for a long time but 2800 sounds to be reasonably slow. A four stroke can easily get down to 1800. Prop pitch has more to do with landing speed and you are already only turning 6" so that should be fine depending on the type of model. I have a Spit which originally flew on an 11x7 but is overpowered on that so I changed to an 11.5x6 three blade to reduce the thrust produced. The bonus is that the landing speed is now much reduced. Quote Link to comment Share on other sites More sharing options...
Roger Dyke Posted June 5, 2021 Author Share Posted June 5, 2021 Hi Martin, Model is propped with an APC 13x6 and peaks at 10,000 rpm. It is propped more for thrust than speed and to keep the noise within limits. It can idle at 2300 - 2500 okay but makes me a bit nervous with recent problems so currently set at at 2700 - 2800. Quote Link to comment Share on other sites More sharing options...
Frank Skilbeck Posted June 5, 2021 Share Posted June 5, 2021 Roger, don't know if your radio has flight modes/phases, if it does you may be able to set the idle trim for each flight phase, I do this on several models and have a dedicated landing phase which has a lower idle setting. 1 Quote Link to comment Share on other sites More sharing options...
Roger Dyke Posted June 5, 2021 Author Share Posted June 5, 2021 Hi Frank, Yes, my transmitter does have that facility. I'll have to have a think about that one. Thanks Frank. Quote Link to comment Share on other sites More sharing options...
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