I'm a little stumbed, I'm trying to get my carb dialed in by changing jetting and there seems to be almost no differences no matter what I do.
Started out with 74s in secondaries- Ran 101.59 & 101.74

Tried 72s- Ran 101.59 & 101.66

Thinking it didn't like going lean I tried 76s- 101.59 (got rained out only run)

So I skipped 4 jet sizes which is pretty significant and ran identical mph. I'm a little confused, I don't know which way to go as it seems such a slight variation could be due to the smallest other variables. Is this normal? What would explain this? How big of a mph difference should I see when tuning with jets?

what do the plugs look like?

whats your intake manifold and your cam those would be helpful too
jon

Plugs look ok. Running a little rich, black around the base ring but no real thick sooty deposits, just the color black. The porcleain on the plugs, however, is black in some spots, and some have this dark tan crusty stuff on it, so i don't know what that tells me.

Combo is a 355- Home Ported World S/R Heads(1.94/1.5) 230/236@.050 solid cam (.471/.485 Lift), 9.5 Compression, Dart/World Sportsman II dual plane intake(nearly identical to edlebrock rpm), and 45ts ac delco spark plugs.

Originally I was running 67/76 jets(650 DP-stock is 67/73) and it fouled the plugs bad, like dark sooty deposits built up on side electrode, switched to 65/74 and ran .7-1MPH faster and plugs cleaned up better(no real big sooty deposits but still black coloring like described before). Then this last outing I played with secondariy jetting and got the results above.

I also found between the last two times out with the identical jetting(65/74), I lost .5-.7MPH even with colder weather, I'm starting to think maybe I fouled the plugs too much and maybe I just need another set and jet down a little bit more.