All you have to do is reinforce areas susceptible to tearing, bridle, balance, form the spine and stress relieve. Find out if your kite shop can get quality kites that measure from between 15 inches and 20 inches wide. This size range is more conducive to western tastes. If your looking for an Indian style manjha truck, buy kites that measure at least 23 inches wide. For durability sake, avoid kites with overly decorative applique`. Tell your dealer you want them un-bridled.
Reinforce the nose and tail of the kite using 3/4 inch clear Scotch tape. Over lap three or four pieces on the nose to protect in the event of a crash. One or two pieces on the tail ought to do it. Arrange these tapes so they stick to both sides of the sail. The tapes can be applied so they alternate both directions, up and down - back and forth, but make sure at least one tape on the nose and tail goes over the end of the spine.
In the area of the kite sail where the nose-leading-edge section meets the bow, there should be paper, Mylar or foil reinforcements. Tape over them with 1 inch long pieces. Arrange these tapes so they are stuck to both sides of the sail, over the bow.
Stick a 1 inch long piece over the spine (back of kite) just under where the bow crosses. Center the tape over the spine and under the bow. This will be the upper bridle point.
Place your finger on the spine of the kite and find the balance point. Identify the point between your finger and the apex of the tail fin. 1 inch toward the tail from that point is where the lower bridle leg will be. Stick a 1 inch long piece of tape over the spine (back of kite) at this point.
With a darning needle and 2 1/2' feet of heavy (9 lbs.) cotton button thread, sew through the front of the kite, two wraps around the point where the spine and bow meet. Make sure the thread goes around both spine and bow. Tie a single overhand knot followed by a double overhand knot, snug but not too tight. Center the knot directly over the spine at the front of the kite. The remainder of the thread should drape down the front of the kite.
Sew through the front of the kite, two wraps around the spine at the lower bridle point. The entire bridle length should not allow the wing tips to pass through. Single overhand, double overhand, snug but not too tight - center the knot directly over the spine on the front of the kite.
Glue the knots. Using Elmers craft bond, or like water soluble flexible drying glue, goop on a little glue front and back to the lower leg and the front only at the upper leg. Let dry and trim the thread tails to about 1 inch. (Tow loop later)
Do this next operation in a draft free area. Hang the kite by the bridle so the spine is level with the floor. In all probability the wing tips will not be level. The high wingtip is the light side and the low wingtip is the heavy side. Add small bits of tape just under the bow - at the back of the sail - on the light side until the wingtips begin to level. Now add appropriate amounts of tape (over the bow) to both sides (front and back) of the sail at the wingtips until the balance is um, "perfect". This both balances and reinforces.
Make a loop with 9 lbs. button thread. The loop stretched out should be about 3 inches long. Larks head the loop onto the bridle. I like to apply the loop so the knot does not obstruct the bridle or the section where the flying line hooks on.
Up to now, you have already done considerable work, so let's take it easy during this next operation. It means the difference between a kite and a wall hanging. Hold the kite at the nose and tail so you are looking at the spine on the back. Slowly draw the kite spine back and forth over the head or knee while applying slight bending pressure. Listen very carefully for cracking sounds. If pressure is not relieved when cracking sounds are heard, they are oft followed by a distinct 'snap'. Impart a slight curve to the kite spine. The majority or deepest part of the curve should be between the center balance point and the area where the spine meets bow.
If that went o.k., it may be safe to bend the nose back a little. Lay the kite on its front. Place your finger alternately on either side of the bow along the spine to use as a fulcrum. Gently bend the nose section back incrementally; just a little. Whew!
Flip the kite over and hold it above the surface of a table by the tow loop. Adjust the position of the tow loop until the tail just touches the table and the nose hovers 1 inch +/- above. Lock down the larks head.
OK, let's get vertical. Test fly the kite by doing horizontal and vertical sweeps at an altitude no less than 20 ft. If your kite will not climb well, adjust the tow loop up in slight increments. Get those sweeps going and check for straight tracking. Give the kite some time so as not to be confused by other variables; gusts, bumpy air etc. There are no guarantees the bow will have a symmetrical spring rate. Example: If on a climb you notice a turning tendency to the left, the bow is stronger on the right side as you view the front of the kite. To stress relieve the bamboo bow, hold the kite viewing the back side. Hook your pinky over the leading edge on the strong side, so you can massage the bow with the thumb between the spine and the nose-leading-edge reinforcements. Stroke back and forth (its kind of like strip milking a cow) and test fly. Repeat as necessary.