Probably going to be looking at something of the 30mm variety.
Any of the OTK products would work well. Also looking at the leading teams/manufacturers, you could also consider something from Merlin, TopKart, Birel, or Arrow and get good support at the track as well.
If OTK, then its the 30mm version. All others, you’ll need to ask an expert on that Make. Topkart seems to do well in juniors and is well supported in WKA. I don’t know what their models are, but call MKP/Topkart USA and ask.
KartLift Kart Stands
DeepSeat Kart Seats
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My daughter runs Yamaha Jr.on a Kosmic Mercury (30mm) and we have had alot of success with it handles well and andjust real well! If you are looking for a OTK 30mm kart they make 3 brands that all are the same otk parts(chevy,buick,cadilac) the tony kart EVK or the FA kart Victory and what we use the Kosmic kart mercury model. A plus to buying a kosmic is that J3 is at all of the big races and they are based not that far from you in erie PA. I have also seen the top karts do well at the track but I dont know the model. If you google kosmic kart J3 Compitition will come up check out there site and look at the models there. Good Luck maybe we can race you next year at the Gopro Motorplex in NC.
I run at those tracks in the Yamaha Senior class and follow the Junior Class very closely. As far as what kart to get I would recommend an Arrow X1E. That is the chassis that I currently use and have had excellent success with it. I also have had great luck with my other chassis of an Arrow X1-28. For parts for the Arrow they are available through Kustom Kart shop who shows up to the track and also can get you the chassis (it is where I get mine from). I also would recommend the Arrow X1E because it was one of the fastest chassis at the last WKA national at GoPro Motorplex with Gresham Wagner.
As far as what the leaders run you are running against 2 very good national people of Brandon Jarsocrack and Austin McCusker (Sorry guys if I spelled your name wrong) both on the Hasse chassis. There are also a lot of top karts in the field but I do not know what models for either the Hasse or the Top Kart.