Help With Honda

[VB-]

trying to help a friend out here, but just cant bring myself to register on any honda forums :laughing-smiley-014:

car is a 98 accord with an F23A, mods are full exhaust and intake (pod). it has a MASSIVE flat spot until ~5k which im pretty sure it where it hits VTEC, then it just takes off till about 6k where it starts coughing and spluttering till just before redline

just changed plugs as old ones look a big fouled up, but made no difference. my mate was telling me that he pulled the leads one by one (replacing the previous one so it only dropped one cylender at a time) and went through that process a couple of times, and both times pulling the number 3 cylinder caused it to die, where as the others just caused it to idle rough

cant be bother throwing it on a dyno but may if its really necesarry. next up i was thinking diagnostic, then fuel filters+clean injectors. to me it feels like spark is braking down but i really dont know where to go from here, and dont wanna do too replacing of things as my mate doesnt wanna throw too much money at it without results.

any ideas?

cheers,

Ben