Hi Donald. For simplicity I’d be looking to go back to the original bvf carb, unless it’s really worn. A 24mm carb on the 125 barrel will provide no benefit, in fact I’ve heard it makes things worse.
Also the new carbs are utter rubbish, I’ve not heard one good thing about them. Im amazed the eBay sellers still list them.
I don’t think I have a spare later carb – lots of earlier ones without the throttle stop screw.