1974 gas series III. Had total bare frame up five years ago but set until i got it about one years ago. Dealing with fuel new stock pump and lines. I had replaced all filters and soaked and rebuilt Weber as i saw lots of junk in first filter. I have run several tanks of fuel through it but lately it is really bucking at times when i come back easy in throttle. Will take wide open throttle like up hill in 4th but it is that easy going from no load to slight throttle input. I noticed today that last filter at carb looked almost dry after shut off and only a little bit of fuel at idle. I have not pulled the pickup tube nor had bowl off the mechanical pump which along with almost everything was new when assembled. All filters look clean now but as i said have never looked in tank. Would one suspect pickup and gum on screen and or screen in mechanical pump as some first things to check? Thank you.