I need to know how much air to put in the front forks

As far as I am aware, the Road king doesn't have air assisted forks. As you have a Harley why don't you go to your local dealer and ask them. But, as Harleys are probably the most modified bike around, it may be worth looking on the forks for a tyre type inflation valve.

The front forks are adjustable to the type of ride you want. First, set the rear shock to the setting you want soft, medium, or hard. There should be max pressure information in your owners manual and on a sticker on the front forks. Typically the most pressure that can usually be put into a Honda front fork is around 14 PSI. Add, carefully, 10-12 PSI using a hand or foot bicycle pump with a gauge on it. You will probably find this way too stiff. Be careful not to put too much pressure in the forks or you will pop the seals and have to replace them.Then with the bike loaded the way you are going to ride (soft for comfort or hard for two up riding) bounce on the seat. What you want to feel is the front and back suspension dropping at the same time. This is how racers set up there motorcycles for hard cornering. If both the front and rear of the cycle drop together you have an easier time controlling the bike during extreme maneuvers. Since the front is usually stiffer than the back(you added pressure there) slowly bleed the pressure out of the front fork tubes until the the front and back drop together while you are bouncing with the bike loaded the way you are going to ride. Now you are set up for extreme riding conditions. Soft or hard that is how you set up all motorcycle suspensions by balancing the the amount of front cushion/pressure to match the back cushion/pressure.

Either you have too much air pressure in your front forks or you ,or someone, has put too much oil in the front forks and you are destroying your forks with every bump. Let out the air pressure to soften the ride. If some one has put too much oil in the forks , disassemble them, evaluate the damage , repair , refill with correct amount of oil , and ride.

Probably the reason the fork seal is blown is too much air pressure. Definitely fix the seal and put in the correct amount of oil. You do not have to put air in to the front forks if you do not want to. To properly set up your suspension, set your rear shocks first, hard for two, soft for one, etc. Now load the bike, you or you and the passenger. With the front forks set to near max pressure (only 12 to 14 pounds air pressure do not go over max recommended pressure) bounce on the motorcycle seat and bleed off the pressure in the front forks till the front and back of the bike drop together. This is the correct way to set up your suspension. A bicycle foot pump with a pressure gauge works best works best. You will be near max pressure in one small hand squeeze of the foot pump. You will find it only takes 7-8 pounds of pressure to set up your bike. Just remember, You do not have to put air pressure in to your front forks, they will work just fine. You just wont benefit from the adjustable design.

First of all do not add oil to your front forks with out draining them first. If you over fill your forks with oil you will damage your forks. To change your oil in your forks, first center stand the bike and lift the front wheel by putting a jack under the motor. Remove the front wheel and axle and put a pie tin under the fork tube. Reach up into the bottom of the fork tube with a hex key and loosen the screw but do not remove. Now take the air pressure cross over tube off, this will allow you to unscrew the fork tops( On some bikes you may have to put a towel on the tank and unbolt the handle bars to get them out of the way.). Pull the screws out of the bottom of the forks and gently pull down the oil should come out now. If you need new fork seals take the lower tubes off and replace(You may need to take off the fender and hang the calipers with wires.). Turn the lowers over and dump out the oil and reinstall fork lowers. Snug up screws and sealing washers on the bottom of forks you can not tighten till you put on fork tops. Now pour in measured amount of oil, again do not over fill. Put on fork tops and air crossover tube. Now tighten screws on bottom of fork. Finish reassembling bike.

are the forks leaking oil? is there air pressure in the forks? Start by draining the forks and putting in the correct ammount of the proper oil, and getting the air pressure right then see how she rides. Other things to check, front wheel bearings, worn triple tree bearings.

FORK OIL
• Place the front fork vertically without spring.
• Compress it fully.
• Pour specified front fork oil up to the top level of the outer
tube.
 Capacity (each leg): 490 ml (16.6/17.3 US/lmp oz)
 99000-99044-L01: SUZUKI FORK OIL L01
or an equivalent fork oil
• Move the inner rod slowly with the special tool ten times and
more until no more bubbles come out from the oil.
 09940-52841: Inner rod holder
NOTE:
Refill front fork oil up to the top of the outer tube so that bubbles
are visible while bleeding air.
• Refill specified front fork oil up to the top level of the outer
tube again. Move the outer tube up and down several strokes
until no more bubbles come out from the oil.
• Keep the front fork vertically and wait 5 – 6 minutes.
NOTE:
* Always keep oil level over the cartridge top end, or air may
enter the cartridge during this procedure.
* Take extreme care so as to pump out air completely.
• Hold the front fork vertically and adjust fork oil level with the
special tool.
NOTE:
When adjusting the fork oil level, compress the outer tube fully
without the fork spring.
 Fork oil level: 153 mm (6.02 in)
 09943-74111: Front fork oil level gauge

Your owners manual will help if you have one. There used to be drain plugs under each fork. The air valves help suspension smoothen the rides more.

dissassemble forks and replace fork seals.(and oil) becareful forks are under a lot of spring pressue. use a workbench vise to hold fork tubes. you will need the manual for this. plus you will need to know the "proper" amount of fluid to put back into the forks.