I recently installed the 330cc big bore kit on my 05 300ex. At the very top of the rpm it revs out and on decel it pops. The throttle response isn’t as crisp as before. I should also note i have a dynojet kit with uni filter, full big gun exhaust, big gun rev box, hotcam stage 1. Stock compression, stock slow jet (size 38) The spark plug is black at base of threads and on the inside walls of the threads. the porcelain is white, fire tip grey. I am fairly close to it dialed in but haven’t hit that sweet spot. I am currently running the 118 main jet (dynojet with dyno needle in stock setting) air screw 3 turns out (dynojet stock setting) the engine slightly stumbles every 5 or 6 seconds. Its close to smooth but not quite there. Im thinking going up on the main jet might clear up the popping but what perplexes me is the black carbon fouling on the inside walls of the threads and at the base. should i go down a size from stock on the slow jet?

who here has experience with the trx 300ex’s with similar mods? any help would be appreciated. the ignition is fine. its just carb tuning the big bore.