put a NOS carb on a Mazda B-2000 (hey, it could be a D50 for reference sake!) and now the car doesnt want to exceed about 50 mph. Its like a rev limiter kicks in at about 3500 rpm, I mean it lays down hard like the ignition cuts out then when I let up on the gas, itll pick right up so I limp it home doing about 1100 rpm in 4th. ITs kinda weird that I drove 140 miles round trip on the old leaky shaft carb and this didnt happen. Is it timing? too far retarded/advanced/mechanical not working? (it times dead on at 8 BTDC with a timing light and advance plugged) Itll buck if I floor it enough to think some one is turning my ignition on and off. Someone told me it may be a plugged cat or muffler, and it aint the muffler because I cut it off and it still does it! What gives? right off the bat I can rev it up but it seems to get worse after it has a chance to "load up" as the plugged cat guy explains. I dont really buy his theory but im shooting in the dark here.