Im no expert but heres my suggestions.
It may be related to an ignition issue. If you have a points type dizzy, check the points and condensor and make sure the timing is correct with a timing light.
Points and condensor are relativley cheap so are a good place to start if the carby's dont seem to be the issue for you.
definatley check both carby's mixtures and make sure they are balanced otherwise you will get some funny things going on.
check the fluid level in the dashpots, and make sure both the float levels are correct in the float bowls. If the float level is too high it can cause flooding of fuel into the engine.
otherwise it possibly could be caused by a blocked or restricted fuel filter or crap fuel.
another suggestion is, if you dont already have one, a haynes workshop manual. there are easy to use procedures to help fault find in these types of situations. very helpful.
hopefully you will find the issue with ease. good luck.

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'66 BRG Morris Mini Deluxe 60HP ATW
