318 running beyond rich

That Holley 1850-3 is a universal fit 600 cfm and should be great on your 318. If it is old and has never been rebuilt, now is the time. When they sit or after they have been heat cycled many, many times, the power valves fail by being stiff and brittle. They don't seat anymore and fuel weeps into the PVCRs causing an over rich mixture. Another serious cause is something a lot of people never think about...the o-ring on the needle/seat assembly. When new, they compress on installation and effectively seal. After sitting or many heat cycles, they become squashed and harder than Kelsey's nuts (whoever Kelsey was). Remove the needle assemblies and check out those o-rings. New ones are in the Holley kits as well as new needle/seat assemblies. Most people disregard them. Here is a fact - and I have no intention of arguing about it with anybody - the viton tipped needle/seat assembly NEVER WEARS OUT! Only that pesky o-ring! That old 600 Holley is one of the most dependable carbs Holley ever made. I think most everyone has 3 or 4 of them laying around! I build on the average 20 of these a year for people. Good luck with the rebuild.
Pat
PS: be sure to use a genuine Holley kit