I have a Stihl FS130 string trimmer. Last year toward the end of the season it got hard to start. Even after you did get it started and had it running for a while if you stopped for a bit it was still hard to start even when it was warmed up. Well it's doing the same thing this year too. Very hard to start even when warm. When you press on the primer button it doesn't seem to build up any pressure and there is not very much gas in the bulb. Once you get it started it runs just fine. No problem at all. Only starting when hot or cold is a problem. What might be the cause of this?