For now, use a 27 venturi. Too big will run fine at high rpm, but will die off quickly when trying to lug.
Take the bowl off and drill out the main jet to .095" - .100". Clean out good and put back together.
Drill out the bottom set of holes in the metering stem a bit bigger than stock. I forget the size - maybe .080" or so.
With the larger main, the load needle will need to be in most of the way.