I had the same problem. I am shooting a 53 lb recurve at 28". I was shooting arrows up to 75/80 pound spine, and could get weak indications.
Orion may be right, but in my case it was a form issue. I think it was worse if I tried to "swing draw".
I was working very hard to get ready for a spring bear hunt, by concentrating on my form, and finally figured out my draw length isn't as long as I thought. Someone posted about that recently, maybe Kirk, about how people over measure their draw length and when are actually shooting, they are much shorter.
When it was all said and done, I ended up shooting around a 63# spined arrow that is about 28" long with a 160 grain two blade. Can't tell you how much money I spent on arrows that were ultimately too stiff.
Keep after it, you will get it figured out.
Good luck,
Gary