An H4 lamp is not designed for a HID lamp. The H4 bulb has an integral shield to limit glare on low beam. There is no "legal" HID conversion made for H4 lamps and never will be: the light pattern can not be correct without a very special bulb and no company is going to invest in that bulb for very few sales. All kits use a "stock" HID bulb made for some car use, most kits modify them so the original lamp won't fit in the kit adapter. It's very possible that getting a replacement bulb that fits will be near impossible, the manufacturers of the cheap kits come and go. No "brand name" company makes an H4 HID conversion... I've seen name brand kits but these were fakes - same crap in a box with a name brand printed on it.
If you want an HID lamp, find an HID lamp assembly from some car and adapt it. If you want bright driving lamps there are HID ones available, they cost $$$ but turn night into day ahead.
On a 750 there is plenty of electricity available to run a 55/65W H4 headlight. Smaller bikes, not so good. Don't try to use the off-road high wattage bulbs. Smaller bikes can use low-wattage (35/35 or 35/50) H4 bulbs in a conversion lamp: the light on the road will still be way better than with the feeb-o-dim stock unit.