Hi, i am having problems with acceleration on my 1987 1500 over about 4000 rpm.The car idles ok and accelerates fine up to 4000 rpm then it starts to splutter and backfire then cut out

I have removed and cleaned the jets and tubes

I have read that you should see a swirt on fuel in the carb when the engine is off but i am only getting a dribble,could this mean i need a new pump diaphragm

Thanks Shaun