ORIGINAL: upsman522
I did bring up the topic of leaning out the mix with him. If i remember correctly, my instructor said that running too lean will shorten the life of the engine and it was good to run with a ''slightly rich'' mix. He did a basic test where the throttle response was good after idling a while, then he lifted the plane and pointed it up and down and all around and it did not stall. Apparently if the engine was too rich throttle response would have been slow. If it was too lean the plane would have stalled when he pointed it all over. He does have the stock tank, it was the first thing i asked him.
As far as i can tell there is no leak, but the tank in the nexstar was factory installed, and getting it out looks like it involves unmounting the engine, something i must admit i am a little fearful to do. So hopefully nothing is wrong with the clunk inside the tank or something like that.</p>
This engine is a FXi, similar to the AX but mine run a little slower for whatever tuning they omitted from those to the AX, I don't know, it just is slower. The holding of the plane upright is to listen to the engine rpm change when doing so, if it drops in rpm, it's too lean, if it increases it's slightly rich or too rich, and if you don't here any change, it's dead on. You'd want to hear a slight increase in rpm, since unloaded in the sky, the engine is going to lean out a bit more than on the ground. It doesn't do much good moving the plane in other directions, just upright, for this test.
The main needle sets the wide open mixture, the idle screw adjusts idle, midrange, and you notice the transition from idle-mid- to full throttle being sluggish or nearly instant, depending on the low speed setting. Change the low needle, then you must readjust the main needle again, and go back and readjust the idle once more, and again the main needle. Turning the idle screw should be done in small increments, in this case you'll want to turn it clockwise, leaning the mixture.
What prop are you using? When you get a short flight time, are you out of fuel and come in dead sticked, or if you remove the wing, do you still see fuel in the tank? Maybe your clunk is stuck.