Thanks for the info. I am replacing all four idle mixture screws with new screws from Holley. I don't have a starting point for the old screws because they were not adjusted properly to begin with. I don't know if the small block carbs would be that much different than your big block carbs but previously I've been told several different settings for the mixture screws on the end carburetors ( anywhere from 1/8 to 1 1/2 full turns open). I know this setting is very precise and an 1/8 or 1/4 turn could make all the difference between a smooth idle and a terrible one. That is why I was asking for information on an untouched, original carburetor, hopefully to unlock this mystery. The problem is, if I get the setting wrong and the engine doesn't idle properly, I still have access to the front carburetor idle mixture screws and they can be adjusted. However, the only way to adjust the rear carb is to take it off and on, adjusting the needle setting each time until it is determined to be right. It is virtually impossible to adjust the rear carburetor with it installed. Does anyone know if there is a "spec" setting on the idle mixture screws for the 4789 and 4790 carbs?
Thanks
Switch the rear carbs back to front,adjust the front then put it back,it will get you real close.There are a few alternatives,someone on here some time ago had mixture screws and a tool to adjust without removing,someone should remember who.The other is replace the rear base with a Promax base with angled screws,a little pricey but it works.
Just got two sets of small block carbs about 20 min. ago,haven't opened yet,I'll check later today and see if they still have plugs,if so I'll find out what you need to know.
