I run mostly 4 strokes with Magnum being my main sport engine.. Recently I have been breaking in a new .70 and having one heck of a time… Probably have close to a gallon through it now… I break them in on the plane.. I have had the engine running great and then all of a sudden it won’t idle etc… I readjust the low end and it is ok for awhile then everything goes to he** again.. The good news is after thinking/saying some very unpleasant things about the engine today I may have discovered what is going on… It’s this darn hot weather… Last go around with this I set it up at home one morning and got it running good.. Took it to the field around 8am… Temp was in the mid 70’s. Engine ran like a clock… Got a couple more good flight off it that morning then around noon everything went to he** again… Temp now around 103…. I just hapened to feel my fuel can which is setting on a flight stand out in the sun.. It is very warm … Not hot but extremely warm… Now the light clicks on…. In the morning the temp and fuel are cool at the engine runs great … As the day progresses the temp/fuel warm up and engine performance starts to deteriorate… By 1 o’clock it won’t idle anymore… Then I reset the low end to try and get an idle so I can continue to fly… Next morning I come out when it is cooler and my adjustments are off again…
Has anyone else run into this problem ?… Were talking temps around 103-105 in the shade… 138 on my little temp thingy pointed at the asphalt.. You guys in Az have this problem ?… Should be some heat experts there….
I also suspect all the “goodies” are vaporizing out of my fuel when I open the can to refuel… A fresh can always seems to run noticeably better… Best solution I can come up with at this point is to put a white towel over the can etc while it is setting there which I am going to try next trip to the field along with a fresh can of fuel… Short of icing it down it seems hard to keep the temp below the ambient temp so I am wondering if fuel is ok even at 105 – 110 degrees ???… Fortunatly we have a cool down comeing in a day or too.. Mid 90’s….