Hi I have the same problem too, I have a 70 zed which has just had a complete resto job including carb rebuild using a Z thereapy kit, carbs were completely rebuilt by a specialist, not only do I get the problem when I brake hard but I can't run the car on choke for more than a few seconds when I first start her up otherwise she coughs and splutters because of carbon deposits on the plugs, the carb guy insists that everything is set up right so I am at a loss, I have spent sooooo much money trying to get this sorted but have now resigned myself to the morning routine of starting the car with enough choke to get her going, then shutting the choke down completely and keeping her running using gentle pressure on the accelerator until she warms up a bit. If anyone has any suggestions to fixing either of these problems it would be much appreciated. Lee