ORIGINAL: gaRCfield
Before I was adjusting my low end based on transition from idle to WOT, and by pinching the line and noticing the reaction at idle. I am now setting the throttle to idle with a tachometer and watching the change, if any, in RPM only at idle setting.If you drop to idle and the RPM slowly starts to increase, you mixture is lean. If it decreases, the mixture is rich.There are different styles of carburetors, but they are accomplishing the same thing - adjusting the fuel and air mixture going to the engine. Both are turned to make the adjustment leaner or fatter, regardless of what direction you must turn each individual one.Again, I posted this because the methods explained in the manuals, i.e. basing the judgement off transition and pinching the fuel line is very subjective - what might sound like a good transition to one may sound boggy to another. Using a tach and watching RPM at idle is objective - look at the numbers and see what they say. Of course with time you can learn to hear the difference, but it's so slight that a beginners ear may not hear the engine slowing down.
Thanks, gaRCfield, now I see.
Yes, I too try to find the minimum idle rpms, but that not always allows a good transition.
As stated above, there is a compromise between both regimens, for which the flame inside the engine remains burning.
At pure idle, there is an optimum air-fuel mix that allows a stable flame at maximum temperature. A little more of air (lean mix) or fuel mist (rich mix), and the flame will cool down until a flame out happens.
During transition, the mix leans itself because the air is lighter that the fuel, and it is easier for it alone to rush into the vacuum of the crankcase. At the same time, this rushing mix is cool and can also induce a flame out when it reaches the combustion chamber.
Nice low idle is easier to achieve for four-stroke, which are helped by the momentum of the bigger propellers that they are able to swing.
Check this link:
http://www.hooked-on-rc-airplanes.co...ning-tips.html
For my two-stroke engines with air bleed, I tune the idle by opening the air screw and reducing the rpm with the radio trim alternatively. The optimum point is reached just before the engine quits due to excess of air. From that position, I start testing the transition. The trick is to run full throttle before and after each adjustment, and also turn 1/8 or less at a time. Instead of stopping the engine for each adjustment, I use a piece of fuel tube and a stick of balsa to manipulate the bleed screw and stay far from the propeller. The blast of air keeps the stick away from it when my hand is not holding it. Dead sticks are history after I began to do it this way.[sm=thumbs_up.gif]