The aftermarket needles are mostly made by Keyster. They run more than 10% lean until 7/8 throttle, so this causes a large 'flat spot' to occur at about 1/8 throttle or so, until more than 2/3 throttle is reached. If you have the OEM needles, use those, for sure.
If the float level is too deep (for various reasons, one being the bike is on the sidestand and not the centerstand), it will make the mixture rich until the semi-stuck float needles dry the bowls out too much, at which point it will die. The only SOHC4 that will idle on the sidestand for very long is the CB350F and some of the early CB400F bikes. These carbs actually rely on some roughness of the pavement and more-or-less vertical orientation of the bike (or equivalent G-force during turns) to feed the fuel to the carbs.
Don't overlook the venting to your fuel supply. If the tank (or bottle) is sealed it will start out rich and dry out soon afterward, going lean. These tanks have vented gas caps to let the fuel drain to the carbs, but the vents can corrode shut in a single winter, especially if gas with ethanol is in the tank (it just happened to mine again this winter).
