buy fitting a larger front sprocket will this slow a bikes acceleration?

[Dan J]

from 12 teeth to 15 teeth

 

[Gort]

all so it will increase MPG at highway speed. 50 --65

 

[Lola]

That would slow the acceleration a lot. And I wouldn't know why you would want to do a mod like that.

 

[LeAnne]

All else being equal, yes - but it will increase the top end.

 

[guardrailjim]

Yes.
Also, depending on the motorcycle model #, there may not be enough clearance to fit a sprocket that large in diameter.