Clipper losing power on load intermittently

My '89 Clipper is currently suffering from a problem where it will drop in revs dramatically when trying to pull away.
This mainly happens when the engine is warm, anywhere from 5-15 minutes after starting.

Once the car has been left for a short period of time, 5 minutes or so, it will start again ok and will run fine.

Other than this issue, the car starts first time and runs well.

It has had the following new parts fitted, in attempts to solve this (and other!) problems:

• Weber carb
• Fuel pump
• Swirl pot
• Fuel tank sender

Any suggestions?

I had the same issue with mine. There should be a flap in the air box that shuts when it's warm. If it doesn't the carb will ice up. Also I changed the distributed on mine too that did the trick.
Good luck