1995, 115 horse Johnson

[tsubaki]

Got a carbed 1995 Ocean Runner that starts cutting out after about 30 minutes of warm up time at full throtle.
It acts and sounds like it is either losing gas or spark and breaking down when trying to apply load after idle and/or when running at full throttle.
The problem is most evident AFTER it has warmed up.
We have;
replaced the fuel cell and all hoses and filters from the tank to the motor and the one in/under the cowl
replaced both coils
replaced the spark plugs as to the book gap/specs
cleaned/rebuilt carbs

It runs, idles and purrs like a dream for the first 30 minutes and then starts acting up.

Any ideas????