restrictive exhaust?

hey guys
just getting our 66 notch re-registered after being off the road for a while!
the motor originally was a single carb but it was playing up so we happened to find some 1500S dual carbs.
these carbs were rebuilt and then installed.
While doing this we put on an NOS type 3 muffler setup and since then the motor hasnt run the same!
the engine is running out of breathe at 30 mph and when u flat foot it nothings happens!!
could this be the exhaust from being so old and the baffle getting clogged up or could it be the wrong jetting in the carbs?
cheers
rhys

Try changing the exhaust back to the old one. If it runs better then its obviously the NOS exhaust. If it doesn't, then most likely the problem is your carbies.

Rhys, when possible and practical, try to get in the habit of changing one thing at a time.

this is dads fault not mine!!!
cheers
rhys

Make sure your dizzy is advancing. Maybe you forgot to hook up the vacumm line when you did the carby swap.

Cheers

Steve

I'll back that up, check the advance 😀