There are two kinds of KJF’s in the world: those that start that way, and those that switch to it. I was referring to the first. If you decide at the beginning of the game “hey, I want to go KJF this game,” then it’s very, very difficult to make it work unless you go all in. This means things like stacking Buryatia with 6 inf on R1, moving 2 inf into Sinkiang, and basing fighters in Kazakh to up the threat to Manchuria; building an India complex UK1; consolidating UK fleet in SZ 30, or taking Borneo, on UK 1; and either building a Sinkiang IC and spending the rest of America’s paycheck in the Pacific, or skipping Sin and going full bore on the boats. If you only do one or two of these, Japan can easily squash them, but with all together it can be too much for them to handle.
I should add the disclaimer that I’ve never successfully won a game this way, nor has anyone beaten me with this tactic. I know some players have been able to make it work, but it’s awfully difficult. You can contain Japan’s Asia expansion, but sinking their navy tends to take a while (unless they defend poorly), and Russia just can’t hold out long enough against a good German player without American assistance (and with only half-hearted UK assistance if they build the India factory).
The second kind of KJF is the only one I use myself. Sometimes Japan gets hosed by the dice on J1; this often happens, for example, if they try to take on too many naval battles at once (e.g. retaking Borneo while still going after Pearl). Sometimes they go Pearl heavy and don’t come out with a strong enough fleet to survive counterattack. Etc. When the dice or opponents’ mistakes give you an opening, you can go KJF to exploit it.
In this aspect I think it’s similar (though in a less extreme way) to KAF. I used to think KAF was completely impossible, but two of my league losses last year were to KAF strategies! (Funcioneta and U-505 both beat me this way.) The thing about KAF is that you can’t do it right away, but if you build up enough transports, have some ground troops in or near Bry, and the USA doesn’t have a lot of ground forces in North America, then you can suddenly switch to KAF and take them by surprise.
In short, my opinion is that you pretty much do have to start every game KGF, and keep your eyes open for the possibility of switching. This might seem like a bummer, but I think it’s actually kind of fun; learning to recognize what combinations of circumstances provide openings for things like KJF, KAF, or other “non-standard” tactics is an important part of advanced play.