There are a number of things that will affect how hard or easy it will be to start your truck, like a bad plug or bad gas. When you block the carb with your finger and start up your truck, you are creating pressure for the fuel to move up to the engine. That takes the place of useing the primer button. Some guys do this because not all vehicles have a primer button. The LST tank just so happens to come with one. Just watch the fuel level when you do use it, just like when you block the carb. Too much fuel will cause it to flood and lock up. If you do decide to use the primer, pump it just untill it reaches the carb, but not into the carb. It should be able to move the fuel the rest of the way.

If the primer doesn't push the fuel up, or the pressure available doesn't pull the fuel to the engine, you may have an air leak. The other side to the primer buttons, are that they can also be the source of air leaks[]. You can remove the primer and plug the hole. That will solve the problem if your primer is leaking air[8D]