ORIGINAL: thailazer
Okay, this Pinch Test worked really well. I've been having problems with an OS Max 25 faltering when going from idle to full throttle. I pinched off the fuel just before the carb at idle and the dang thing ran for over 20 seconds. As I went to lean the idle mixture screw, it had no resistance at all, it was that loose. Can't believe it backed itself out so it must have been that way from the factory. I have about 40 flights on the engine. Looks like doing the pinch test on a new engine is a good idea as I simply flew it rich for the first few flights to break it in and then leaned the main mixture valve without touching the idle screw. Thanks to all that commented.... great to have all these experienced forum members.
You've just illustrated beautifully why glow modelers
need to have some basic understanding of how and why an engine works, and of how to tune it. Sure, if you buy a more expensive brand like OS or Saito they generally come set fairly close to right straight out of the box, with only the high end needing tweaking but there's always that monday morning/friday afternoon engine that's wrong, and settings can and do change with use. It's for the same reason that you should follow a sensible break-in procedure even with engines whose manufacturers claim it's not required.
Glad it's worked out well for you - you've learned a useful skill and can now look like the resident engine guru at your local club by passing it on.
