You ONLY tune an engine when at Operating Temperature. Main needle/HSN *first* and idle/midrange mixture *second* to get a fast throttle transition from idle to WOT. Indeed set the main needle/HSN with WOT runs until it cuts out or the RPM sags then back off 1/8th turn rich. If you're getting that hot on a WOT run you're on the edge of too-lean if it isn't cutting out. However, Do NOT rely on the temp gun to tune your engine. They are prone to inaccurate readings. It's always best to tune by ear. Forget smoke trails as a tuning aid at first as not all fuels smoke the same when burned. Also the glow plug heat range can affect the smoke amount. I will say the smoke color typically will be grey if lean and blue if rich. If the idle hangs after a WOT run for a short time, the idle mixture is too rich and the idle gap too wide. This can cause (and often does) all sorts of tuning problems.
Last edited by 1QwkSport2.5r; 03-24-2014 at 09:33 AM.