300ex Running Issue

Hey guys, I’ve fully rebuilt a 1997 TRX300EX from the frame up and I cannot get it to run correctly. It seems like it’s an air/fuel issue but I cannot for the life of me figure it out. It does idle and will run through all the gears smoothly but as soon as I let off the gas it will instantly turn off, I usually have to turn on choke to get it going again. It does this almost every time I try to take it for a test ride, if I stay in low rpms it won’t die out, it’s not until I really rev it out and let off that it will turn off. I’d also like to note when it is at idle and I crack down on the throttle, the throttle response is not perfect and at idle it will bog out if I push the throttle down too quickly, if I push the throttle down slightly slower it will rev out fine. However, when reving it at idle, it backfires and pops quite a bit on the deceleration. Something I’ve found strange with this quad is in order for me to even get it to run where it’s at now, I had to increase both the pilot and main jet size and change the needle position to allow more fuel delivery. It wouldn’t even idle and rev out with the stock carburetor internals and setting. As far as I know the engine is stock, I did rebuild the top end with the original size piston and cylinder. As far as performance parts it has a uni foam air filter and an extremely free flow DG RCM full exhaust system, the header is basically a hallow tube and the muffler I pulled apart and repacked. Also I wanna note I’ve tried other carburetors and the one currently on it is brand new and the aftermarket jets I installed are also new so I don’t believe it’s any sorta clog or delivery issue from the carburetor. The valves and seals have also been replaced seared and adjusted. I really just find it strange I’d have to increase the jets just to get it running where it’s at now. I’m just looking to see what anyone else thinks, I’m open to any ideas on the possibilities of why I would need such big jets just to get it running the way it is and also why it’s still not running right? From my own perspective I feel like maybe I’m missing some major air leak? Or maybe there could be an aftermarket camshaft inside that I’m unaware of, I kept whatever camshaft that was in it during the rebuild but I didn’t measure lobe size or see any indicators of it being aftermarket. I also don’t know if an aftermarket camshaft would cause this type of issue either. If you have any idea please let me know, this thing is driving me crazy!