My Ryobi 705r strimmer won't run !

If by fuel pipe you mean fuel line, yes, this could cause the problem your having. The jet that you referred to is more than likely the needle valve that sets under the diaphragm.
So, go ahead and replace the fuel lines and make sure that you get the correct sizes for both. One may be smaller than the other, depending on the size of the trimmer. (TIP: Before feeding the fuel lines into tank, cut the lines at an angle, making it easier to insert into gas tank holes. Once you have them where you want them, cut square.)
One fuel line goes from the carb. to the bottom of the tank, with the fuel filter attached at the end inside tank. This line should rest comfortably on the bottom of tank.
The other line goes from the primer bulb to just inside the gas tank, (about 1/2 to 1 inch), with coupling attached to the end.
If this doesn't solve the problem, and I believe it will, let me know. And when you respond to this comment, try to respond through the comment button. For some reason, I didn't get an e-mail from your comment. I just happened to stumble on it when going over my solutions.

Thanks for the rating Mike. If you should have any questions about "Drywall Finishing/Patching, or know someone who does, put your questions to Category:Tools- Building & Power- Hand Tools" at Fixya.com

Jim If by fuel pipe you mean fuel line, yes, this could cause the problem your having. The jet that you referred to is more than likely the needle valve that sets under the diaphragm.
So, go ahead and replace the fuel lines and make sure that you get the correct sizes for both. One may be smaller than the other, depending on the size of the trimmer. (TIP: Before feeding the fuel lines into tank, cut the lines at an angle, making it easier to insert into gas tank holes. Once you have them where you want them, cut square.)
One fuel line goes from the carb. to the bottom of the tank, with the fuel filter attached at the end inside tank. This line should rest comfortably on the bottom of tank.
The other line goes from the primer bulb to just inside the gas tank, (about 1/2 to 1 inch), with coupling attached to the end.
If this doesn't solve the problem, and I believe it will, let me know. And when you respond to this comment, try to respond through the comment button. For some reason, I didn't get an e-mail from your comment. I just happened to stumble on it when going over my solutions.

Thanks for the rating Mike. If you should have any questions about "Drywall Finishing/Patching, or know someone who does, put your questions to Category:Tools- Building & Power- Hand Tools" at Fixya.com

Jim

i have the same problem how but its not my gas line when i reduce the choke it dies i have the same problem how but its not my gas line when i reduce the choke it dies