what size Accelerator Pump carb

[stretch]

I am considering a swap to a carb with an accelerator pump on a stock 125.
would those of you with more experience recommend a 27mm or 30mm carb?

 

[stretch]

or would both be too large for a stock 125?

 

[Cactus Jack]

It depends on if the carb has a round or oval bore ... Oval bore carbs are smaller in flow than their outlet bore so a "30" Mikuni for instance is actually a 26 mm carb... You add the height and width of the venturi at the slide together then divide by 2 to get the actual carb size ... Round bore carbs are the actual size of the round bore ...
Your inlet port size is what you should measure ... A "27" oval bore carb or a 26 mm round bore carb will work great with a 26 mm intake port and 27 mm inlet valve ...