I'd say that it all depends on the spring that's on the engine. If it's a single the best bet would be to take the rockers off that cylinder and hook an air hose to the spark plug hole so that compressed air can be used the keep the valves closed. Then use one of those spring compressors with the hand wheel on top to compress the old spring and remove it. Keep track of the keepers with a magnet. Then compress your new spring with the tool just enough to allow you to get the keepers back in place. Don't go too far or it's harder to prevent the keepers from escaping before you back off of the tool and allow the spring to extend back up to it's installed height.
How tight it is probably depends on which spring is the one that is broken. Is it toward the front? Toward the rear? Or in the middle of the engine next to the shock tower.....
If you don't have a compressor, I've heard of stuffing a rope down into the cylinder (leaving some of it sticking out), then ease it up to tdc and rope'll keep valve in place. Change spring, turn crank backward some, and pull rope out.
if you can not find the stuff to hook air up to the spark plug hole I have another thing you can try. Take the plug out and run some rope down in the hole. It has to be small enough to fit the hole, but big enough it will not get pinched at the edge of the piston. By hand rotate the piston all the way down. Put as much rope as you can in and then rotate the piston up.
Make sure the rope is kind of soft, and make sure you take the rocker arms off before you start with the rope.
unless i was told wrong an its somthing else wrong wat do ya think if i can crank it up an it idel nice an smooth but if i hit the throttle its like it start missing an i can hold it to the floor an it wont go over 3000 rpms