The way your post reads is that you have a 26p prop with a 13" diameter running 2:1 gear ratio. The gear ratio may be correct but there is no way it is a 26p on a motor that small. We really need more info. Look at the prop again and confirm the pitch. Tells us how many rpms you are running now, speed, condition of current prop, and what you want to accomplish by swapping it out ie better holeshot, more top end, etc.