Stock needle settings are not terribly important. I don't even bother learning the stock needle settings for my engines anymore; I just drip some extra oil into the cylinder, lean the carb until I can get it started the first time, enrich the carb until it can barely hold an idle, then start slowly leaning it again after the first couple tanks of fuel.

If it's running at 280F, either the mixture is too lean or the compression is too high. If you can't enrich the fuel mixture to cool off the engine without making it choke when first accelerating, then you need to add a 0.2mm shim to the cylinder head to lower the compression a bit. RC-Willpower sells shims for GO engines; the easiest way to find out which part to order is to email them from their website, and they'll tell you which part you need.

However, if you've been running it at 280F for a long time (more than a few runs), then the piston will already be broken-in to fit properly at 280F, and you'll have to replace the piston and sleeve to get it to run properly at a lower temperature.