Carbed Spider stalling under load

[PilotInASpider]

Hi all, this is my first post about my 1979 124. It has the 2000cc engine and stock carb .I bought it with a bad head gasket and have successfully changed that, the timing belt, water pump, and valve cover gaskets. I just got the cooling system properly bled (woohoo!) and took it for a test drive.
My problem is that when I get around 3k rpm under load it just stalls. If I put the clutch in and pump the gas I can stop it from dying but it feels like there's not enough fuel going into the carb and thus it's stalling when I try to accelerate past 3k. It idles fine and accelerates well until it loses power and cuts out. My guess is it's a carb issue but any input would be great.
Side note: I am currently running a straightpipe that is cutoff around the middle of the car. Don't worry I will be putting a real exhaust on it but the PO bent the header and I had to cut the downpipe from the midpipe to get things clear of the steering. There is also an open bung for an o2 sensor on the header that I haven't plugged yet. Not sure if my exhaust setup would cause this sort of issue. Any help diagnosing the issue would be greatly appreciated!

[SteinOnkel]

We repair carburetors. It sounds like yours needs a good thorough cleaning.

Shoot me a pm and we can work something out.

Thanks
Steiny

[Nut124]

The bowl could literally run empty.

Check the fuel pump, lines, filters, hoses. Put a fuel pressure gauge in line at the carb and run it on a hose to the wiper so you can see the pressure while driving when this happens.