Difference between Slide needle in Premium kit and N65C

Something doesn't sound right for your A/F to be going that lean in the midrange. Is your slide drilled larger than the supplied bit (>7/64)? If the slide was drilled with a 1/8th or larger bit the slide is opening too fast. You can sometimes control that by using the longer stock spring but most times the only remedy is to replaced the slide.

A N65C needle will be richer just off idle but leaner in the upper-middle of the circuit compared to the needle we have in the tuners kit.

Hi I resized and uploaded your dyno sheet. While I may be somewhat of an expert with carburetors this chart isn't clicking with me. I'm used to seeing dyno runs that show RPM (rather than MPH) and certainly never have an A/F spike this large. My experience tells me that a spike that large would definitely be felt and not go unnoticed as you indicated to me by email (said the bike runs strong, no hesitation). The chart lacks any significant dips in torque or HP coinciding with rise in air:fuel.

As I recall "Run Type: RO" refers to a Roll On test so perhaps this is contributing to why this reading doesn't look right??? (I'll let other's who know chime in). Again, I'm not a dyno expert so I may be reading this completely wrong. I would prefer to see the A/F charted at either full throttle or a slightly less cruise RPM (preferred) as opposed to a roll on test. I would not start messing with the jetting until I understood what was going on with these numbers.

What I find odd is that the HP/TQ curve has no change when you go lean at mid way.

The MPH thing is a bit different, I'd like to see it printed out over RPM as well at least that's the way I've always looked at the charts, can you operator reprint it with TQ/HP on top of each other on one graph with AFR below and RPM as the bottom constant.

The only thing I could think is happening is that the slide is popping up then not
lifting properly in the mid range until the engine reaches a specific need of velocity/vac
and can force it open, leaving the needle down in the main tube during that position and
hurting fuel delivery... as the engine RPM picks up past a specific point the velocity is sufficient to raise the slide... allowing the fuel flow to increase in the upper rpm/mph range.

That's just a wag though...

Get a different slide and try it,

Ken (not me, the OP) contacted me and found there was a leak at the petcock vacuum hose. Problem appears to be solved.