I think that the sense of this thread is that you need to develop a feel for how engines react to various levels of priming. While an experienced modeler may have 50 years of starting these little beasts to draw from, there is no reason the newer hobbyists can't benefit from that pool of knowledge.

While I feel it is best for the new guys to use a starter, it pains me to see how little they know how to best use it. Far to often I see them throwing the prop and spinner off the front of the model because they over-prime then attack the airplane with the starter in hand.

While a too dry engine will not readily start, the signs of a too wet engine is having the prop come loose when you put the starter to it.

All of these problems go away if you just develop a bit of feel for the engine and installation. Not every engine is the same, nor do they like the same thing. But generally, once you find out what a particular engine likes and you do the same routine, then they will reward you with easy starts. You know, where you can fuel up, go to the flight line, and get a one flip start.

The backwards snap start or backwards bump takes a slightly wetter prime to work. It is also the right direction to use if your prop is slightly loose, since when it fires it also tightens the prop nut. You will know when this happens, because your prop will be in a different position relative to closing on compression than it was before you start. If the prop has moved, then check to see that you still have clearance on the spinner cutout to the prop. You do not want the spinner to contact prop.

I however prefer to flip the prop, unless I am using a sharp edged prop like the APC. Wood props work best for this, since they are fairly dull on the edges. So I will fuel up, open the throttle and choke the carb while pulling the engine over two or three times. Then I flip the engine a couple of times before putting on the glow plug igniter. When you put on the plug driver, you want the engine to be out of the compression zone where the prop turns freely. Anyway, at this point grasp the prop and slowly turn the engine over through the compression cycle. If primed well, it should give you a bump as the piston reaches top dead center. Turn it over again, and if it bumps again, then the engine is over primed, so continue to turn it over by hand slowly.

When the engine gives a bump on one rotation, then no bump on the next it is ready to start. At this point either use the starter or flip it by hand because it has the right amount of fuel to start. Either way, it will not toss the prop.