Acceleration Flat Spot

[john116]

Hi All,
Just a carb question - my 58 Mercury with 430ci engine and stock 4BBL carb has a flat spot on accelerating from idle. I know this is a classic faulty accelerator pump symptom, however, I checked the accelerator pump diaphragm and it seems to be intact. When watching down the throat of the carb, minimal fuel gets ejected from the accelelerator pump jets on gentle acceleration. A decent quantity only comes out on moderate to hard acceleration.
Thanks guys.
John

[Theo]

Had a similar problem until I found out that the fuel bowl was dirty w. metal flakes and other debris. These particles can get between the needle and the seat. Anyway you might check this first before you burn out your brain

[Shelby#18]

How about the fuel pump shaft being worn? It would be a quick check to disconnect the hose after the fuel pump to see if it is pumping out the correct volume.