Weber carb accelerator pump diagram needed . Not pumping .. anyone? ??

Sounds like restricted fuel flow...new correct fuel filter? Air/Fuel mixture...while idling...turn each screw clockwise until slight stall...then back out (counter clockwise) one and a half turns to smooth idle...Hope this helps.

if stock its in the fsm
if not ,it not.
alldata.com
look there. if stock and in usa.

Sounds like the accelerator pump circuit in the carb is not squirting fuel in when you depress the accelerator. That is why you get the lag in acceleration before it decides to launch. When you open the carb you should get a steady stream of fuel from the accelerator pump. With the engine not running look down the carb throat and open the throttle blades and visually check to see that there is a stream of fuel when doing so. If not time to rebuild the carb, or just get another accelerator pump for
the carb.

1977 ? egr valve is leaking, or the accelerator pump on carb is bad

check for stuck advance weights in dist. Check accel pump in carb

I take it that the distributor has a set of points and if so check the dwell angle to set the point gap
if it has electronic ignition check the rotor gap for the exciter and check the exciter operation
more costly parts will not solve the problem as car manufacturers use aftermarket parts in an OEM box just to inflate the price
stumbling on acceleration can be from incorrect ignition timing ( should be 12 degrees BTDC) or a problem accelerator pump/power valve in the carby
holley carbs came with different settings on the power valve and others have an adjustment on the pump linkage
hyt leads should be of high quality in the area of the insulation and plug gap should be correct
check that the coil is wired correctly and that the voltage is correct as it will be running a resistance wire from the ignition switch to the coil to reduce the 12 volts to 7.5 volts when running
low mpg is determined by driver habits but you can check the float level, cat converter for failure and blocking the exhaust and transmission changes are correct for rpms and road speed ( vacuum actuator on the transmission if auto)

Just taking a shot here as I have seen the same thing in the shop in that last month....I am going to throw you two scenarios as you don't say if it has a carb or F.I.
If it is Fuel Injection the filter or a weak pump would be the culprit.
If it is a carb engine there is an item called an accelerator pump. this pump pumps fuel into the throat unmixed so during startup and on acceleration it needs this raw fuel, on startup to just get fuel into the chambers and on acceleration when switching from the Idle to the venturi there is a dead spot that this pump covers for.. A 20 dollar rebuild kit for the carb is all you need. there should be a tag on the carb for the ID to give to the parts store..

IS THE TIMING SET CORRECTLY?

it sounds like the points are not opening enough. or to much timing. thats to far advanced timing. but points most likely good luck.

I would change gas brands, it may be an additive they use, have seen this before on my own car, a 1973 NOVA, I went to a carb shop they sold me a Viton rubber pump, changed gas brands installed the pump and problem went away.