If it takes a few seconds then its very rich. When you pinch the line fuel is cut off immediately, however if very rich it takes a while for the extra fuel clinging to the crankcase walls and bottom to disperse. If its off just a little the engine picks up in a fraction of a second.
Sport_Pilot,
hmmm....I'm talking about idle mixture setting. How do you explain if the engine just slows down and quit without increasing the rpm? Isn't it too lean? It still takes a few seconds. I'm not talking about the high speed mixture, in which case the result of pinching is instant.
Also in this "lean" condition, sudden opening of throttle results in engine quitting. And if this is "very rich", why would engine run better if it's further enriched?
I appreciate and value your comments/advice very much. So please don't take this as combative. I say this because when I read back what I wrote, it does look a little combative...but I don't mean that.
I usually pinch approximately 3/8" to 1/2" before the inlet. I wonder if we are talking about the same thing.
I'm quite sure I'm within 1/4 turn from the optimal, more like 1/16 turn, or 1/8 turn, unless there are more than one peak in idle mixture setting, in which case, who knows, I could be way off!
If you are going to use the low nitro fuels, and pretty rich setings,
you might try a hotter plug. That will give a less tendancy for the
fire to go out.
Flyboy Dave,
I changed the glow plug to Tower Hobby from SuperTigre (both of them make only one kind of glow plug) the last time I was at the field. It did make it better for both high speed and idle. btw, the top rpm was 13500 with MA 11x5 which is over 1.28 BHP, according to Thrusthp.
Tower Hobby's plug is equivalent to OS A8, A3 or in between, depending on who you talk to. I should get A3 and A8. so I can make a comparison.