Briggs and Statton engine problems?

Hi, Help please..... I have a Briggs and Stratton engine(8HP, 319cc Vertical crank, Model 190707 /Type 1189-1 Code 80080709) which is very difficult to start - and if starts runs rough and is now cutting out when warm and wont restart.
This is fitted on a ride on mower - I have disconnected all the electrics to the mower but no change.
I have fitted a full carb refurb kit and new spark plug no change.
I set the air jet (Top of teh carb) to 1 turn and the mixture jet to 1 1/2 turns..
The compression measures 120Ib cold and is similar hot.
So.... what am I doing wrong? All ideas appreciated , Thanks Garry

Garry Brandon
May 2009