Cuthbert42

VIN JYA31M003DA002869 build date 3/83 milage 53914

I have seen people use a small section of red spray straw from a can of carb cleaner siliconed into a hose connector as a restrictor.

One question that comes to mind is, have you checked the valve clearances. It doesn't matter how clean you carbs are if your valves are out of spec. When that is done, clean the carbs yourself, most shops have no interest in properly cleaning 30 year old carbs, you'll also learn a lot more about your bike if you do the work yourself. Just my two cents.