i use them and love them.
the leancondition that these solve are the float bowl running out of fuel at high rpms.
they come in different sizes.eg. 190 to 250 depends on the hp levels. if you go with one that's too big .at idle they would flood the engine as fuel would leak past the seat. if you go too small fuel bowl would run dry at high rpm.
you need to experiment with different sizes to get which is best for you .you can also calculate your fuel consumption and figure out the correct size for your application. i hope this help everyone understand these a little better and give them a 2nd chance.
p.s. they don't use very high fuel press. about 2.5 to 3 psi.