whats the deal?

Ok guys, with all my other builds getting the mixture right was not a problem. Ive used this carb before on other bikes and have found the right jet pretty easily. Usually the most power is one step richer from too lean (white plug).

The thing about this setup is it doesn't seem to be able to run lean.

Not that I want this bike to run lean, but ive always thought that with the right spark plug, running too lean will make the plug white and too rich it will be dark brown or black. On this build, i have moved all the way to an NGK B5HS (pretty hot) and using a #53 jet the bike still seems to run fine and the plug is brown. Ive tried jets ranging from 53 to 72 and the most power seems to come when using a 58 jet, but the plug doesn't get darker or lighter from going up or down from this "ideal" mixture.

There is very little power difference from jets from 56 to 65, which doesent make much sense to me, even more confusing is that the plug doesn't change color (ive used other plugs too).

I found that with the stock HT carbs, if I make the jet size too small, the engine just won't start until I get the jet size close to where it's supposed to be. (then I drill it a little bigger)

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thats what is so weird, the engine runs with this huge range of jets and soesent seem to run very differently either way