Carb Jetting

I need to hear from some carb guys. Last weekend I was at the track for some test and tuning. I was rejetting my 650 after every couple passes and pulling plugs. After my last pass I pulled the number 2 plug and it finally looked like I had the right burn. Plug was nice and tan. Figuring I had the right setup I pulled the number 5 plug. It was white as the day i installed it new. Is this something that is common with a carburated car? Middle plugs tan, end plugs white (re: lean)? My primaries are jetted at 72 and my secondaries are at 78. This is up from a lean 66/72 out of box carb. Should I bump my primaries up to match my secondaries?

Got to be someone on here that knows carbs.

Dark Knight said:

It's normal for the end cylinders to run leaner..
what power valve are you running, and is it a double pumper or vac. carb?
did your MPH change at all?

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Don't know what the power valve is. I assumed its standard Holley valve for a 650. The carb is a QuickFuel ProVac. Meaning, it a vaccum secondary carb. My MPH did change. With the out of box carb the jets were 66/72 and my best ET was 13.6 @ 100. With jets changed to 72/78 my last pass at 1:30 in the afternoon on a very hot track (96* and very humid) was 13.2 @ 104.25. Ran a couple of 13.2's earlier in the morning with smaller jets and had 1.8 60' times. The afternoon pass my 60' was 2.0. (Spun in first and second)
I've been thinking of trying to stuff a little taller air filter in the open air, air cleaner and jet the primaries to 76. I'm thinking if I equalize the jetting front to rear and move a little more air to the carb I might get a more even burn across the cylinders.