I am presently shooting beaman bowhunter 500 arrows with 145 grain heads. I would like to add weight to the arrow without changing the spine. How effective is adding rope inside the arrow to gain weight?

i believe any change to weight will effect spine no matter where you install it

Any weight added to the shaft will change the spine. Remember, there are two types of spine. Static and dynamic. Static is what you get in the tester, dynamic is spine in motion. Adding weight to the front changes spine by resistance to forward motion. Adding weight along the length of the shaft results in loss of spine by making sluggish recovery in paradox. Think of adding weight as the difference in two different weight fellows. The lighter weight fellow can turn with a quick spin. The heavy fellow will most times have to take a step in the turn.

I'm currently have the same problem. Normally I shoot 400 def. shafts with 145gr point. Now that I want a heavier arrow with more FOC I've found that I'm having to use 300def. shafts if I want to use the 250gr point.

Troy

Troy is right on the money with this one (as usual, good to see you posting here again, Troy).  If you are going to play around with adding weight to your current set up, try paper.  Cut a sheet of computer paper in half and roll it up so it fits inside the shaft and then let it unroll inside the arrow.  If I remember right standard paper adds about 35 grains per half sheet.

tubes or weed wacker or rope all add weight and all will make the arrow act weaker.

I tried rope, Weedeater line and weight tubes. All were aggravating in various ways. Finally settled on steel adapters and broadhead weight to get a decent weight (10 gpp at least) and FOC. Adjusted for bare shaft arrow flight slightly weak by arrow length. For even greater FOC I add brass inserts.

Think about stepping up from the bowhunter shafts to the MFX's....KK sells them by the 1/2 dozen so it doesn't break the bank to do this.