Here is the Jet kit. It comes on the slow boat from china. Or you can order from in the states and it will be here fast but cost more.
One thing to keep in mind the supporting vendors are in state and will make sure you get the right parts or make it right ever time.
The same cant be said for china stuff.
https://www.ebay.com/itm/10Pcs-Carbu...53.m2749.l2649
What are your RPMs doing are they high or is the engine bogging?
NEO is right that you wont be able to get a good read without your intake on.
Im no expert by any means but it seems that a lot of the newer buggies were sent out with smaller jets 112 and 114 I think I even remember seeing a few posts with ones that had a 108 main.
A 120 with a UNI mod is an OK place to start but its only that a starting place. You have to read the plug and adjust the jets to get where you are supposed to be.
How did the buggy run before the upgrade other than the smoking?
Is it reaching high RPM quickly or is it taking a while to get there?
If its hitting high RPM but your not getting speed then its probably not your jets
If its boggy and slow to climb to higher RPMs then jets are a good possibility but not the only one.
Spray some carb cleaner around your intake if it falters then you have an intake leak.
I know you just bought a new one but even new ones can leak.
If its reaching high RPMs quickly
You may also pull your CVT cover and see if you belt is traveling up and down on both pulleys like it is supposed to. If its not that could also be the cause of you low power.
Even if one of these is what's causing your issue you still really need to get the jetting correct. Rich will foul your plug. Too rich will diesel and wash your cylinder walls and you will end up with gas in your oil and damage to your cylinder and piston. Too lean and you will fry your rings.
Get back to us with what you find out
I will throw out suggestions but remember im not an expert just trying to help
NEO and others on here are experts and give great advise they really know their stuff but the more info you can give about the symptoms and what the motor does the faster they will be able to help you sort out the problem.
The main goal is to get you out riding and enjoying your buggy again.