I have a 6cyl in my 62 chev that will not run on top end its like the accelerator pump in the carb is out it wont handle quick throttling it just sucks air til fuel finally catches up but when u drive it it wont get up and go like it should but it idles great and .i rebuilt ehe carb and its doing the same thing it did before the rebuild.new tank good gas and points and plugs in it .