Dear Bill,

My OS FS-70 Ultimate does not have a reliable idle after 25+ minutes or so of running at full throtle very rich and leaning frequently. The engine ceases to run at idle and seems too rich when I try to increase RPM. When the glow plug iginition is on it runs ok. I turned the idle needle clockwise about 90+degrees but no result. I also tried to make it richer by turning counter clockwise by 45 degrees but no result either. I'm using 10% nitro and 18% Klotz oil Model Technics fuel and 13x7 APC prop. I can not figure out where the problem is. This is very strange for an OS engine. I'm a bit disappointed to tell you the truth.

-According to the manual the carb is adjusted for 15% nitro, do you think that I should use more nitro or some other kind of fuel such as Cool Power?
- The engine is inverted, does it matter?
- Also according to the factory setting the idle needle screw gap should be at 12 o'clock, however mine was at 10 when I put it out of the box. Do you think that there is a wrong idle needle setting from the factory and I have to readjust it according to the manual?

I really look forward to your reply,

Thanks and regards,

Nick

ps: If anyone rather than Bill could help, his advice would be more than wellcome.