Did 20-25 degrees drop in air temp make the engine act different?
You will be surprised how the air temp will affect the engine performance. It will make a difference. I also would try adding another washer under the glow plug. Sometimes when the engine runs good for a while and then starts to overheat, try removing your needle valve and plugging your vent hole on your gas tank and flush your fuel line. I just experienced a slight overheating yesterday and I flushed the line and after that everything was a-ok. Any little particle wedged around your needle valve will choke off some fuel and will cause a leaning effect which could cause an overheat situation. Im running 15%nitro and and keep my needle setting at about 2 turns thru 2 3/16 turns. Usually the warmer it is outside, Im running at a slightly richer setting (2 3/16). I have four washers under my glow plug. Seemingly this has been the charm for my engine ever since it was broken in. At about 1/4 stick Im Hovering to slightly climbing (depends on the wind) half stick, its full throttle. Go with three-four washers under the plug, Lean it out and back off about an 1/8 of a turn. The only thing you should be doing once you get a full flight in without overheating is adjusting the needle valve according to outside temperature and if you do have an overheat, flush your fuel line. I havent had to tinker with my V7 much at all except for adjusting needle valve for temperature change and flushing the fuel line. Sometimes its good to check your glow plug every now and then because they do over a period of time wear out. Also they develope a crystaline on the glow coils which will affect plug performance. if you are really careful, you can remove the crystaline with a straight pin or pointed tooth pick. take real care not to damage the coils. Out of three gallons of gas I have sucessfully cleaned my plug coils of this stuff about three times and each time noticed a noticable change in engine performance.