Hi My Kingston L4 needle valve seat is hairline cracked in 2 places and leaking. What can I do? Langs is out of L4's for months. Teflon tape did not work. JB weld, Permatex fuel proof gasket sealer?
Can you post a picture of the cracked area? Are you talking about the seat that the float needle fits into?
You can do this:
@Mark the body that the the needle valve assembly screws down on.
Doesn't sound good, sounds like it got cracked when somebody used too much force in the past removing the assembly (they can get pretty stuck after many years). I think Royce's recommendation will get you going faster than trying some kind of fix on your cracked body casting.
If you want to stick with a Kingston carb, Dave Huson has a bunch of Kingston carbs for sale, see his listing on the classifieds: