2004 Switchback 800 VES Problem / Please read and provide some thoughts

I have a customer with this machine ( I am a self employed power sport mechanic). It has a low end bog off idle only. By that I mean, if the sled is over 2,000 it runs fine. It doesn't hesitate at all if the motor isn't idling.However if you punch it off idle it hesitates and has a slight backfire through the exhaust. Let me start with what I have done. Keep in mind the current owner did not buy it new so we don't know any prior history. The previous owner confirmed it had the same issue the whole time he owned it.It has under 2,000 Miles.

1. cleaned the carbs 4 times with my ultrasonic cleaner
2. reset the fuel and air screws to factory defaults 1 and 1
3. tried tuning the fuel and air screws with little results
4. Both cylinders have 140 psi compression.

One thing I did notice is the PTO side cylinder is running about 60-80 Deg. hotter than the magneto side (Tested with digital infrared therm)

I am assuming that the PTO side cylinder needs to be richened but I have never had to run one cylinder that much different than the other on any machine I worked on. Or what about the crank being out of index?

Any thoughts/ideas would be appreciated !!!

Thanks, Mark

I forgot to add, The sled has the factory jets in it with the factory exhaust. Also, I did clean the power valves and they are seated and sealed correctly.

I reset the needles to the factory recommended setting. #4 position (from the top).

I did recalibrate the tps and checked the reeds. I also did check the carb fuel and air screws, the ends aren't broken.. Same issue. I am stumped.