Back to the subject:
I'm not entirely sure what Karash is experiencing, but if it is what I think it is, then it's normal. The problem lies in the fact that the Ki-84 has a very low speed limit permitted for the first notch of flaps, and it will retract over 165 or 170mph IAS or something like that.
Now, the Ki-84 is certainly a very agile plane, but frankly it is nothing special if the flaps aren't in use. As a matter of fact, there is a small speed margin of about 30mph, between about 170mph IAS to 200mph IAS, where the plane is extremely vulnerable to destabilization due to low speed and high AoA, but cannot use the flaps yet. Some veteran pilots say they don't notice that much of a problem, but for many people this speed range is a very dangerous point in which the Ki-84 is momentarily hindered in maneuvering - until finally the speed drops low enough to deploy the first notch of combat flaps.
This is most noticeable when you are duelling a competitive pilot in perhaps a Spitfire or a N1K2.
The Ki-84 with flaps out, is very vesatile, able to match the turning radius of the Spitfire or the N1K toe-to-toe with much more stable handling. As a matter of fact the Ki-84 turns better than the N1K2 and most Spitfires, barring the Spit5 and the Spit1 in pure radius. The problem is when the engagement starts out with some speed, in an attempt to enter tight-looping verticals with lots of rudder use, often leading to a rolling scissors situation.
The enemy N1K2 or Spitfire, in defense, enters a very tight looping turn in the vertical and the Ki-84 pilot is often compelled to follow it. What happens is the Spitfire or the N1K2 goes tightly vertical, and then easily "snaps" downward using the gravity and momentum, entering a full circle pattern of flight.
The Ki-84 tries to follow it, but when he has reached the apex of the tight loop his speed is still not low enough to deploy the flaps. Therefore, the Ki-84 is momentarily destabilized, and refuses any pitch input from the stick - which attempt if enforced, will cause roll axis destabilization that 'wallows' the plane. Therefore, the pilot has no choice but to leave the Ki-84 hovering for a very short time until the speed drops down 170mph IAS, and then he can pull the flaps out and immediately "snap" downwards to continue the loop.
Unfortunately, that split-second of a delay is enough to lose some serious ground in the tight maneuvering contest, and by the time the Ki-84 has flaps out and starts moving downward, the Spit or the N1K is already climbing back up towards your tail.
Also, even if you didn't lose enough ground to lose the fight outright, when you are coming down from the apex of the climb your speed rises again, and the flaps will retract. This often makes it impossible to keep the angle necessary to stay behind the Spitfire or the N1K, as the Spit/N1K will start going up in another loop, but your Ki-84 cannot pull enough pitch angle to stay in an advantageous position. This is perhaps the one weakness which pilots can fully exploit to defeat the Ki-84 in a similarly maneuvering plane.
...
My advice is, if you will go into an engagement against a Spitfire or a N1K, then commit yourself only when the speed is sufficiently low. If you are chasing a Spitfire or a N1K that is running away at - let's say - about 350mph TAS, then this might bring out the situation as described above, where the Spit/N1K will enter a tight maneuvering evasive, but the Ki-84 cannot follow it directly due to flaps not being able to deploy yet.
In this case, use your E and 'corner' the enemy some more, until he starts resorting to very tight turns and low speeds. Once you are confident that the ensuing maneuvering contest will rarely put your speed above 200mph IAS, then commit yourself, dump all unnecessary speed, and let those flaps rock the world. Once you are in the 'flaps' domain, nothing short of the Hurricane or a Zero can defeat you in it. Just becareful of those 'similar' looking situations which puts you in and out of that domain.
