87 z28 305 carb. new plugs, fuel pump, fuel filter, adjusted timing (now right). MAPLight is being coded. i know i need a new one of those. get on highway, 35mph i stop it down. slow but when i hit 50mph or so, car falls on its face like i just left off the gas and shifted to 2nd gear. let up on the gas it will smooth out but can't put hardly any gas on. does MAP sensor affect it that much or is the prob in the carb. have been having prob with the choke. another note, have to pump the gas about 20 times and it takes 2-3 volleys of this to start the car cold. once it starts, it works fine (still cold). thanks.

 

Starting problem sounds as if your choke is not setup correctly for the initial startup and not closing all the way. Is the check engine light on all the time?

 

yep. shows code 34. the choke was replaced prior to me getting this car. it was 45 degrees out of adjustment. its better but still not right. need a new carb.

 

its either a fuel issue or timing, just because its timed right doesnt mean its firing right, check all the wires make sure their on good shape and make sure that the dist is firing right. not to say you are wrong, but trust me its worth the 10min to double check again before u go anyfurther.

i agree that it sounds more like the carb thou, i had a similar problem when i put my 350 in, she would run beautifully, until the secondaries would open then she would just kill herself, turned out when i had rebuilt it i accidently put the old metering rods back in instead of the new ones. so with a fresh carb threw her on and she ran perfectly. no sensor will effect that engine if its a carbed engine, if you know the carb needs replaced anyways i would do it, or if your up to it rebuild it and take it to a local garage to be fine tuned(try the older garages, find some of the guys that were actually trained on carbs). it sounds like to me the cars getting to much gas and just wants to flood itself, might also try just disabling the choke all together, use starting fluid if you have too and see if it makes a difference, i dont know which kinda carb u have so i cant tell u exactly how, but most carbs its fairly easy.