I have a 509 with AFR heads top mount 2.3 whipple.Every time i go to throttle it up it coughs and sometime dies.It only does this off idle.Brass vent is clean.Tps sensor is at 0.52.Idles fine.After 1200 rpm runs great.When you start it.It does not go 1200 rpm then idle down,it starts and stays at 750 rpm???

Simple, needs more fuel added - you have lean sneeze. Its difficult to get off idle mapped correctly without going to the dyno, even then most dyno guys say you can't load the boat that much down low or their dyno won't hold the hp at that low of rpm and it gets adjusted in the boat.

Actually it can be made plenty fat to start with, but then you'd whine about the soot.

Its an easy fix. Where are you located? Maybe we can find someone to go for a boat ride with you.

800 xcr I live lafayette ind. If its a fuel issue i will send it to dustin at whipple.???

If Dustin did the original reprogram, he's the guy. If not, it may be passworded by whoever programmed it and there may be some trial and error as the only way to change it if you don't have the password is to erase it and start over. Let me know, I'll send you in the right direction.

I,am running fuel pressure at 45-47 w vac hose off.Do you think i still need to raise it.Plugs look good.The IAC valve moves when you throttle up.If its moving is it working right.????

Your problem is fairly common. If it only does it off idle when being put under load - it needs more fuel. Your fuel pressure is plenty high. The IAC won't typically cause a sneeze, it will cause irratic idle, but not a sneeze. Add fuel. Was your setup put on a dyno and mapped?