prosnd

I went out on my first cruise of the year yesterday. After changing a sea (lake) water pump on my Volvo duo prop setup. The engine ran great, plenty of power, no problems, Good top speed and rpm.
Today I changed the oil (redline synthetic) and took it for a ride. It ran great at part throttle cruise, 3500 rpm. When I gave it a little more, it started popping and breaking up. If I opened it all the way up, it seemed fine.
The engine is as follows.
1995 Gen V 454. L29 heads last year and a Holley dual plane with Holley 4160, 750 vac sec carb, also new last year.Timing 30 deg total. ( ran great that way last year)
The carb has stock jets in the front with a 6.5 pwr valve. Secondary metering plate is the richest they make. The carb is set up so that at 3500 I am on the primary's only with a closed pwr valve. Above that the secondaries start to open and the PV opens.
I guess my question is where should I start looking for the source of the pop and breaking up? Does it sound like water in the fuel? Could it be that the good ride yesterday mixed the water up and it is just showing up as a problem today. Yesterdays good running ride was only a couple of miles at most in open water and a 1/2 mile each in and out of the cove at no wake speed.
Thanks for all the great advice I am about to receive.
Charlie