So i have a 91 Accord with a f22b1 VTEC motor from a newer accord, the guy who owned it before me did the swap and instead of using a vtec ecu he wired in a vtec control box, when i got the car it ran like a top and vtec pulled nice and hard. Here lately when i hit 4k where vtec engages it will pull lightly but not as hard as it used to and the rpm needle will bounce forward and back and all over the damn place and vtec gets really weak and studdery ( sorry but thats the best way to describe it i cant seem to come up with an explanation of what could be causing this weakness, before vtec engages the car runs like a top like normal. A buddy of mine said something about maybe the clutch slipping? but im not too terribly sure

If anyone has any recommendations of things i could check or replace would be a real help

thank ya