You should have a tensioning device on your wheel. The most common tensioning is Scotch tension where a piece of string goes from the "mother of all" on one side across a special groove on the bobbin and down to the other side where it is adjusted with a "key" shaped piece that turns in a hold, held by friction. This creates a drag so that the bobbin actually spins a bit slower than the flyer and this difference makes the yarn draw in. There is also Irish tension which reverses this, flyer tensioned and bobbin freer. Finally there is the double drive method where the bobbin and flyer are both driven with the same string, but due to different diameters, the difference is achieved. The "mother of all" can be adjusted by pulling it away from the wheel or allowing it to go toward the wheel, (either traditional or castle type wheels.)
If you send us a picture, we can tell you what type of tensioner your wheel has and how to adjust it.