Main jets can be changed.
Several sizes fitted to various FoMoCo carbs.
You should have a tube on the
carb overflow nipple. Black stiff plastic which comes out to the inner wing,
the large hole in the suspension tower, and secured with a tie to the cross bar.
Overflow can happen when the engine suffers from heat soak after switch off,
fuel expands a bit and seeps out down the tube.
Derek UK