Exciter 440 carb help needed

[Pinto]

I ran across an extremely clean 1979 exciter 440 and couldn’t pass it up. It runs ok but has a midrange lean condition. A little choke makes it come out of it. I’ve had the carb off and apart many times and it’s spotless. No plugged passages, it all looks perfect. Looking at the plugs it also looked to me like it was a little lean at full throttle too. The Kehein carb has a 90 pilot and a 165 main jet. Looks like stock the main should be a 152. Given that it was already jetted richer than stock and still lean I figured there was a good chance of an air leak or bad crank seals. I ended up pulling the motor and had the crank rebuilt because a main bearing was rough. Put it back together with new seals, gaskets, piston and rings. I noticed someone had done some porting on the cylinders. It still runs the same as it did before, Lean in the middle and top end.
Im not sure where to go from here. Find a different kehein? Swap to mikuni? Oil injection has been deleted and I do have a 38mm mikuni from a junk sled I could put on. Not sure where to start on jetting for the Mik though.

Thoughts?

 

[74Nitro]

Is the airbox completely stock?
Also, is the rubber adapter boot between the airbox and carb in good condition.
These will be lean if either of those is not stock or in poor condition.

 

[Pinto]

Is the airbox completely stock?
Also, is the rubber adapter boot between the airbox and carb in good condition.
These will be lean if either of those is not stock or in poor condition.

Rubber boot is new. Air box is stock. Only thing is I’m not sure if there is supposed to be foam on the outside of the air box or not.