Engine runs fine for an hour or so then starts to sputter and stall, I have changed fuel fiter, and added octane booster

Jim Keel, August 2009

if ok for an hour, not fuel filter, and octane boost is a waste of money, and could even of made it more of a problem.
Possible fuel mix, over heating, check your water paths, is enough coming out, might be restricted a bit. so takes time to over heat. Mix not quite right? sound something along those lines

sheepdog, September 2009