RE: Glow Plug Idle Bar
The history that I have heard is that the idle bar is a holdover from the days when glow engines were open exhaust, without mufflers. The idle bar was necessary to get a decent idle, lacking the backpressure a muffler provides.
Like many a beginner(some 21 flying seasons ago) I used some idle bar plugs in my first engine, a K&B .40. That is until the scolding I got from experienced members for using such a plug! I was told then, and I have found, through countless flights and no telling how many engines over that twenty one year period, that idle bar plugs are completely unnecessary in modern engines. I have seen instances, in fact, where the idle bar came off the plug and trashed the piston and sleeve.
I was a serious pylon racer for a number of years (at least I thought I was) and as such, through experimentation, I identified one plug that works the best all around. The plug that delivered the best performance and longevity, even under the brutal conditions of pylon racing is the McCoy MC9 (also marketed as the Hangar 9 MC9). I have flown entire seasons on the same plug, sometimes longer than that! As for idle reliability, well, let me just say that some of the races were won or lost based on whether you were able to earn the bonus point for landing and coming to a complete stop with the engine still running.
As far as for 4-strokes, my plug of choice will always be the OS F. I have flown two seasons with both a YS .63 and an OS 1.20 Surpass III and I am still running the original OS F plugs. By the way, that is with 30% all synthetic oil fuel.