I have been posting this issue over in the setup section but i think this is a better place to discuss what my problems are. I recently bought a 2000 520 vx with a 225 optimax on it, no jack plate. I've been working on getting the boat setup since last monday. It came with a 4 blade trophy plus on it and ran 62, 63 mph at about 5350 rpm. I figured, well 25 4 blade is a bit big, it needs a 25 3 blade and i'm in business. I bought a 25 Tempest plus, put it on and the result is very close to the same. It did do 64 mph once and it might have hit 5400 rpm a few times but, pretty much ran the same as with the 4 blade. Obviously something is wrong under the hood. to give you some background, the boat has sat for about 2 years. It had 3/4 tank on one side and probably 1/2 in the other. I filled both tanks and put a double shot of quick kleen in and figured it just needs run. I emptied 1 tank, refilled it with high test and another 6 ounces of q/k and it still runs the same. I checked the plugs and they seem fairly clean.
Things I've noticed, even if you over trim it the rpms won't go over 5400. Also if you hit the trim switch in either direction it seems to loss power, like its starving for voltage.... It doesn't kill the motor it just looses a few rpm. It has a new battery in it but the battery is only 500 cranking amp. could this be the problem?