My grandkids have karts. Both have 5 hp Briggs engines but different
models of Briggs. Both engines dies when you let up on the gas quick
and get back on it quick. He has a third engine he switched out but
it does the same thing. Two are from centrifugal pumps and one from
a Montgomery Ward rototiller. They are older engines.

Any ideas what is needed to fix these so they don't die when
accelerated quickly? There are high speed adjustments but no low
speed settings. They seem to be lean when they die.