This is interesting. While my two FP's on profile ships restart fine, where this might help me is with my Fox 35 on my Cobra. Starts very well the first flight, and runs beautifully after Paul helped walk me through shimming the intake port. But subsequent flights see starts that are time consuming.
I got to the point of being able to hot start my Foxes very reliably. I don't guarantee results but, this is in a Nobler, cylinder down. Attach battery, pull through forward with choke, finger completely covering the intake. Keep pulling through forward with finger over until you get one bump. The, immediately, flip forward while removing your finger. If you don't do it fast enough, or you pull your finger too soon, you will get too much (not fast enough) or, not enough (too soon).
If you do get too much, take out the glow plug, flip it over forward a bunch of times, put the plug back in, then attach battery and flip forward.
It doesn't work on a profile (but what are you using a Fox on a profile for?) and I have all sorts of problems getting all types of engines started, hot or cold, when mounted upright.
I think the only reason this works on a Fox is that the intake stack is short enough that it doesn't hold a lot of fuel. When I first got my ST46, I tried the same technique, and when I went to flip it, I almost broke my finger, because it was hopelessly flooded to the point of hydraulic lock.
Note that this was, to my astonishment, *40+ years ago*, but my condition makes me recall it like yesterday, and physics and chemistry haven't changed too much since 1978.
In all these cases for hot starts, the critical matter is to get *just enough* fuel in the engine to get it to bump without getting too much. The tolerance for "too much" is nearly zero, even a little bit over with some engines, and you are in trouble. The Fox is particularly tricky and notorious for bad hot-starts, but I that is all I flew back in the day and got flight-after-flight-after-flight as fast as I could put in the fuel, and, I couldn't flip it over if necessary because I was using a stooge.
With big ABC/AAC engines I never ever flip them forward with the battery attached, but I it safe enough with the Fox and a wood prop. Back-bumping is the only safe way to start them with your fingers, and it also has a lot more tolerance to excess fuel, because it blows the excess backward out the venturi. Even a pretty good Fox tends to have such low compression that it doesn't easily fire off with a back-bump.
In almost all cases, the trick is to get just the right amount of fuel
Brett