Keith is no dummy, he puts the carb on his engines that work the best...A larger carb will not make it run any better..If it did he would put it on there...
The HDA62 came from a Zenoah Red Max G4K hedge trimmer...
WT 250 11.1mm bore
HDA 62 12.7 mm bore
the WT 76A I thought might be on there has a 13.49 mm bore, used on almost all 3.2 size engines..
A larger carb making more power is mostly wishful thinking...A G62 has a 15.08 mm carb on it...I put a SDC80, 19.05 carb on one...NO DIFFERENCE at all......
Go with what the manfacturer set it up with, he knows more about his engine than we do.
A G26 runs the same, within 100 rpm, with a 3/8 carb as it dies with a 1/2 inch carb..Been there.....[8D]