Thanks for all the info. All good reading, but I guess the real reason for the question is I have recently acquired an O.S. 15 LA and have not been able to get it to run for longer than 2-3 seconds. I started with 15% Cool Power MV and am now trying SIG's 1/2A fuel which is 25%. The longest run was on the 15%. Glow plug (A3) is good and I've replaced it just to make sure and it appears to glow quite well. I live at approx 5800ft. and haven't had any problems with my O.S. .46 AX. My assumption was that since the 25% was designed for 1/2A it might do well in the little .15. Not so. WJVAIL and DOWNUNDER have done a great job in explaining why this is not necessarily so. Can anyone point me to a thread or give me some info on this little thorn? I was really looking forward to putting it in a HOB Laser Stick or maybe a Spacewalker.