been working on a 72 240z twin carbs setup.

i had the thing all nice and tuned and the guy decided he needed to take the intake and exhaust off shortly afterwards. while doing that he removed the smog pump, air port (injection??) from the exhaust manifold and replaced it with a header. as well as removing and putting plugs on parts of the intake where hoses no longer went.

after about 1/2 hour of me screwing on it i was able to get it to start. but the carbs are wither gone now, or completly out of sync. i cant get the thing over 3500 rpm either.

i can start it, and ill rev the motor and it will go right above 6 come down then acts like its either misfiring or hitting a rev limiter and just stutters till it dies.

just changed

plugs, wires, cap, rotor

car came with a crane gold hei box and electronic ignition

now has a header instead of the original smog type exhaust manifold.

any ideas on where to go from here?

Reset your carbs.

Get it running and make sure that you don't have any vacuum leaks. You did make significant changes to the intake and exhaust, so it stands to reason that you will need to make carb adjustments.