i have a 300cid straight-6 (according to some, one of the top 10 engines ever made!) , with a Offenhauser intake manifold, a mild "RV" cam and a a 500cfm Edelbrock carburetor.
I heard from other posters that Edelbrock carbs out of the box may be set up rich. I installed an Air/Fuel gage and with the assistance of the Edelbrock video entitled "Additional tuning", I started experimenting with different tuning combinations.
Out of Edelbrock boxing has an .86 jet with 65/52 rods, I switched first to combination #6 below with no discernible difference in performance or mileage, just yesterday I switched to #10, 3 stages leaner both cruise and power mode , detected flat spot and A/F mixture went to 17.5 and I ended up with #11, two stages leaner with both cruise and power mode--power mode leanness can result in detonation so maybe next step is to go to # 12 on chart (I would need to order the metering rods as #12 metering rods (.067 x

.049) metering rods) are not in kit.




My set up: With Offenhauser intake and a mild cam: .83 main jet 65 x 52main metering rod,(and orange spring) .095 secondaries




Leaner in order:

#7 .86 with 68x52*

#13 .86 with 70x52

#12 .83 with 67 x49

#11 .83 with 65x 52*

#10 .83 with 67 x 55*

*in kit
Anyway, here are some pictures

 

These are .083 primary jets ( the incriptions need a magnifying glass)
For changing metering rodsou only need to remove the top of the carburetor, to change jets you have to take the top off with a torx screwdriver.again the Edelbrock online videos are very hopeful. It is very important to know which linkages to take off and it is mandatory to use needle nose players for the tiny clips.
3 stages leaner, A/F meter and flat spot confirm this.
Two stages leaner.
Idle A/F between 12-14
Metering rod, jet and spring kit
500 cfm Carb with auto choke

 

Did you get the carb dialed in the way you want it?