I think that I will try the 5% nitro in my engine...I have used 10% and 15% in the past with best results with 15%. The instruction booklet that came with the engine states that 0% to 15% will work fine. My ST engine is now on a  plane that I don't fly so often anymore and I am now enjoying the OS four strokes engines on my other 2 planes. If I could buy a good carb for $40, I think that I would do it. All of my ST engines have had air leaks around the low speed needle end. The new one that I just bought has a high speed needle that you can turn at will and it has little effect on the performance of the engine and yes I put the tubing over part of the high speed needle adjustment to possibly prevent other air leaks. I am hoping that I can do a google search for where I can buy the Perry carb. Thanks</p>