Read earlier in the thread what you have there is not marked NT Speed and is different than the original witch was 16mm I still have one of both,The one you have there is a revised version probably to suit the 4 stroke engine it was really intended for.
No I'm sure pre 2014 the speed carb was bigger but in 2014 Grubee had E.P.A. issues and the speed carb didn't pass so they started using the one you describe with the petcock on the fuel inlet witch is only 15mm and a 14.9 mm slide.
Heck yeah why not. 1mm doesn't seem like alot but sure makes a difference.
You only bore through the main body and to open it 1mm in dia is only a 1/2mm taken from the walls,I've opened the cns carb from 16 to 18mm no issues and the nt and speed can be enlarged pretty easy.
Yeah, just looking there is a little room but not a lot.
Very true but it's a cheap easy way to see if the larger dia helps before actualy buying a bigger carb.
